Re: Regression in throughput between kvm guests over virtual bridge
On Mon, Nov 27, 2017 at 09:44:07PM -0500, Matthew Rosato wrote: > On 11/27/2017 08:36 PM, Jason Wang wrote: > > > > > > On 2017年11月28日 00:21, Wei Xu wrote: > >> On Mon, Nov 20, 2017 at 02:25:17PM -0500, Matthew Rosato wrote: > >>> On 11/14/2017 03:11 PM, Matthew Rosato wrote: > On 11/12/2017 01:34 PM, Wei Xu wrote: > > On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: > This case should be quite similar with pkgten, if you got > improvement with > pktgen, usually it was also the same for UDP, could you please > try to disable > tso, gso, gro, ufo on all host tap devices and guest virtio-net > devices? Currently > the most significant tests would be like this AFAICT: > > Host->VM 4.12 4.13 > TCP: > UDP: > pktgen: > >>> So, I automated these scenarios for extended overnight runs and started > >>> experiencing OOM conditions overnight on a 40G system. I did a bisect > >>> and it also points to c67df11f. I can see a leak in at least all of the > >>> Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the > >>> fastest leak. > >>> > >>> I enabled slub_debug on base 4.13 and ran my pktgen scenario in short > >>> intervals until a large% of host memory was consumed. Numbers below > >>> after the last pktgen run completed. The summary is that a very large # > >>> of active skbuff_head_cache entries can be seen - The sum of alloc/free > >>> calls match up, but the # of active skbuff_head_cache entries keeps > >>> growing each time the workload is run and never goes back down in > >>> between runs. > >>> > >>> free -h: > >>> total used free shared buff/cache available > >>> Mem: 39G 31G 6.6G 472K 1.4G 6.8G > >>> > >>> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > >>> > >>> 1001952 1000610 99% 0.75K 23856 42 763392K > >>> skbuff_head_cache > >>> 126192 126153 99% 0.36K 2868 44 45888K ksm_rmap_item > >>> 100485 100435 99% 0.41K 1305 77 41760K kernfs_node_cache > >>> 63294 39598 62% 0.48K 959 66 30688K dentry > >>> 31968 31719 99% 0.88K 888 36 28416K inode_cache > >>> > >>> /sys/kernel/slab/skbuff_head_cache/alloc_calls : > >>> 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 > >>> cpus=0,2,4,18 > >>> 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 > >>> cpus=0,10 > >>> > >>> /sys/kernel/slab/skbuff_head_cache/free_calls: > >>> 13492 age=4295073614 pid=0 cpus=0 > >>> 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 > >>> cpus=1-19 > >>> 6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 > >>> cpus=4,8,10,12,14 > >>> 3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 > >>> pid=0-11605 cpus=5,7,12 > >>> 1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 > >>> 2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 > >>> cpus=4,12 > >>> 1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 > >>> 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 > >>> 3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 > >>> pid=9915-11581 cpus=8,16,18 > >>> 2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 > >>> pid=11605-11699 cpus=2,9 > >>> 1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 > >>> pid=331 cpus=11 > >>> 8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] > >>> age=8545/62184/110571 > >>> pid=11863 cpus=0 > >>> > >>> > >>> By comparison, when running 4.13 with c67df11f reverted, here's the same > >>> output after the exact same test: > >>> > >>> free -h: > >>> total used free shared buff/cache > >>> available > >>> Mem: 39G 783M 37G 472K 637M 37G > >>> > >>> slabtop: > >>> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > >>> 714 256 35% 0.75K 17 42 544K skbuff_head_cache > >>> > >>> /sys/kernel/slab/skbuff_head_cache/alloc_calls: > >>> 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 > >>> /sys/kernel/slab/skbuff_head_cache/free_calls: > >>> 255 age=4295003081 pid=0 cpus=0 > >>> 1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 > >>> 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16 > >>> > >> Thanks a lot for the test, and sorry for the late update, I was > >> working on > >> the code path and didn't find anything helpful to you till today. > >> > >> I did some tests and initially it turned out that the bottleneck was > >> the guest > >> kernel stack(napi) side, followed by tracking the traffic footprints > >> and it > >> appeared as the loss happened when vring was full and could not be > >> drained > >> out by the guest, afterwards it triggered a SKB drop
Re: Regression in throughput between kvm guests over virtual bridge
On Tue, Nov 28, 2017 at 09:36:37AM +0800, Jason Wang wrote: > > > On 2017年11月28日 00:21, Wei Xu wrote: > > On Mon, Nov 20, 2017 at 02:25:17PM -0500, Matthew Rosato wrote: > > > On 11/14/2017 03:11 PM, Matthew Rosato wrote: > > > > On 11/12/2017 01:34 PM, Wei Xu wrote: > > > > > On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: > > > > > > > > This case should be quite similar with pkgten, if you got > > > > > > > > improvement with > > > > > > > > pktgen, usually it was also the same for UDP, could you please > > > > > > > > try to disable > > > > > > > > tso, gso, gro, ufo on all host tap devices and guest virtio-net > > > > > > > > devices? Currently > > > > > > > > the most significant tests would be like this AFAICT: > > > > > > > > > > > > > > > > Host->VM 4.124.13 > > > > > > > > TCP: > > > > > > > > UDP: > > > > > > > > pktgen: > > > So, I automated these scenarios for extended overnight runs and started > > > experiencing OOM conditions overnight on a 40G system. I did a bisect > > > and it also points to c67df11f. I can see a leak in at least all of the > > > Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the > > > fastest leak. > > > > > > I enabled slub_debug on base 4.13 and ran my pktgen scenario in short > > > intervals until a large% of host memory was consumed. Numbers below > > > after the last pktgen run completed. The summary is that a very large # > > > of active skbuff_head_cache entries can be seen - The sum of alloc/free > > > calls match up, but the # of active skbuff_head_cache entries keeps > > > growing each time the workload is run and never goes back down in > > > between runs. > > > > > > free -h: > > > totalusedfree shared buff/cache available > > > Mem: 39G 31G6.6G472K1.4G6.8G > > > > > >OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > > > > > 1001952 1000610 99%0.75K 23856 42763392K > > > skbuff_head_cache > > > 126192 126153 99%0.36K 2868 44 45888K ksm_rmap_item > > > 100485 100435 99%0.41K 1305 77 41760K kernfs_node_cache > > > 63294 39598 62%0.48K95966 30688K dentry > > > 31968 31719 99%0.88K88836 28416K inode_cache > > > > > > /sys/kernel/slab/skbuff_head_cache/alloc_calls : > > > 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 > > > cpus=0,2,4,18 > > > 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 cpus=0,10 > > > > > > /sys/kernel/slab/skbuff_head_cache/free_calls: > > >13492 age=4295073614 pid=0 cpus=0 > > > 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 > > > cpus=1-19 > > >6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 > > > cpus=4,8,10,12,14 > > >3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 > > > pid=0-11605 cpus=5,7,12 > > >1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 > > >2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 > > > cpus=4,12 > > >1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 > > >1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 > > >3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 > > > pid=9915-11581 cpus=8,16,18 > > >2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 > > > pid=11605-11699 cpus=2,9 > > >1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 > > > pid=331 cpus=11 > > > 8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] age=8545/62184/110571 > > > pid=11863 cpus=0 > > > > > > > > > By comparison, when running 4.13 with c67df11f reverted, here's the same > > > output after the exact same test: > > > > > > free -h: > > > totalusedfree shared buff/cache available > > > Mem: 39G783M 37G472K637M 37G > > > > > > slabtop: > > >OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > > 714256 35%0.75K 1742 544K skbuff_head_cache > > > > > > /sys/kernel/slab/skbuff_head_cache/alloc_calls: > > > 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 > > > /sys/kernel/slab/skbuff_head_cache/free_calls: > > > 255 age=4295003081 pid=0 cpus=0 > > >1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 > > >1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16 > > > > > Thanks a lot for the test, and sorry for the late update, I was working on > > the code path and didn't find anything helpful to you till today. > > > > I did some tests and initially it turned out that the bottleneck was the > > guest > > kernel stack(napi) side, followed by tracking the traffic footprints and it > > appeared as the loss happened when vring was full and could not be drained > > out by the guest, afterwards it triggered a S
Re: Regression in throughput between kvm guests over virtual bridge
On 11/27/2017 08:36 PM, Jason Wang wrote: > > > On 2017年11月28日 00:21, Wei Xu wrote: >> On Mon, Nov 20, 2017 at 02:25:17PM -0500, Matthew Rosato wrote: >>> On 11/14/2017 03:11 PM, Matthew Rosato wrote: On 11/12/2017 01:34 PM, Wei Xu wrote: > On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: This case should be quite similar with pkgten, if you got improvement with pktgen, usually it was also the same for UDP, could you please try to disable tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? Currently the most significant tests would be like this AFAICT: Host->VM 4.12 4.13 TCP: UDP: pktgen: >>> So, I automated these scenarios for extended overnight runs and started >>> experiencing OOM conditions overnight on a 40G system. I did a bisect >>> and it also points to c67df11f. I can see a leak in at least all of the >>> Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the >>> fastest leak. >>> >>> I enabled slub_debug on base 4.13 and ran my pktgen scenario in short >>> intervals until a large% of host memory was consumed. Numbers below >>> after the last pktgen run completed. The summary is that a very large # >>> of active skbuff_head_cache entries can be seen - The sum of alloc/free >>> calls match up, but the # of active skbuff_head_cache entries keeps >>> growing each time the workload is run and never goes back down in >>> between runs. >>> >>> free -h: >>> total used free shared buff/cache available >>> Mem: 39G 31G 6.6G 472K 1.4G 6.8G >>> >>> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME >>> >>> 1001952 1000610 99% 0.75K 23856 42 763392K >>> skbuff_head_cache >>> 126192 126153 99% 0.36K 2868 44 45888K ksm_rmap_item >>> 100485 100435 99% 0.41K 1305 77 41760K kernfs_node_cache >>> 63294 39598 62% 0.48K 959 66 30688K dentry >>> 31968 31719 99% 0.88K 888 36 28416K inode_cache >>> >>> /sys/kernel/slab/skbuff_head_cache/alloc_calls : >>> 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 >>> cpus=0,2,4,18 >>> 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 >>> cpus=0,10 >>> >>> /sys/kernel/slab/skbuff_head_cache/free_calls: >>> 13492 age=4295073614 pid=0 cpus=0 >>> 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 >>> cpus=1-19 >>> 6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 >>> cpus=4,8,10,12,14 >>> 3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 >>> pid=0-11605 cpus=5,7,12 >>> 1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 >>> 2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 >>> cpus=4,12 >>> 1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 >>> 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 >>> 3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 >>> pid=9915-11581 cpus=8,16,18 >>> 2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 >>> pid=11605-11699 cpus=2,9 >>> 1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 >>> pid=331 cpus=11 >>> 8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] >>> age=8545/62184/110571 >>> pid=11863 cpus=0 >>> >>> >>> By comparison, when running 4.13 with c67df11f reverted, here's the same >>> output after the exact same test: >>> >>> free -h: >>> total used free shared buff/cache >>> available >>> Mem: 39G 783M 37G 472K 637M 37G >>> >>> slabtop: >>> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME >>> 714 256 35% 0.75K 17 42 544K skbuff_head_cache >>> >>> /sys/kernel/slab/skbuff_head_cache/alloc_calls: >>> 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 >>> /sys/kernel/slab/skbuff_head_cache/free_calls: >>> 255 age=4295003081 pid=0 cpus=0 >>> 1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 >>> 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16 >>> >> Thanks a lot for the test, and sorry for the late update, I was >> working on >> the code path and didn't find anything helpful to you till today. >> >> I did some tests and initially it turned out that the bottleneck was >> the guest >> kernel stack(napi) side, followed by tracking the traffic footprints >> and it >> appeared as the loss happened when vring was full and could not be >> drained >> out by the guest, afterwards it triggered a SKB drop in vhost driver due >> to no headcount to fill it with, it can be avoided by deferring >> consuming the >> SKB after having obtained a sufficient headcount with below patch. >> >> Could you please try it? It is based on 4.13 and I also applied Jason's >> 'conditionally enable t
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年11月28日 00:21, Wei Xu wrote: On Mon, Nov 20, 2017 at 02:25:17PM -0500, Matthew Rosato wrote: On 11/14/2017 03:11 PM, Matthew Rosato wrote: On 11/12/2017 01:34 PM, Wei Xu wrote: On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: This case should be quite similar with pkgten, if you got improvement with pktgen, usually it was also the same for UDP, could you please try to disable tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? Currently the most significant tests would be like this AFAICT: Host->VM 4.124.13 TCP: UDP: pktgen: So, I automated these scenarios for extended overnight runs and started experiencing OOM conditions overnight on a 40G system. I did a bisect and it also points to c67df11f. I can see a leak in at least all of the Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the fastest leak. I enabled slub_debug on base 4.13 and ran my pktgen scenario in short intervals until a large% of host memory was consumed. Numbers below after the last pktgen run completed. The summary is that a very large # of active skbuff_head_cache entries can be seen - The sum of alloc/free calls match up, but the # of active skbuff_head_cache entries keeps growing each time the workload is run and never goes back down in between runs. free -h: totalusedfree shared buff/cache available Mem: 39G 31G6.6G472K1.4G6.8G OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 1001952 1000610 99%0.75K 23856 42763392K skbuff_head_cache 126192 126153 99%0.36K 2868 44 45888K ksm_rmap_item 100485 100435 99%0.41K 1305 77 41760K kernfs_node_cache 63294 39598 62%0.48K959 66 30688K dentry 31968 31719 99%0.88K888 36 28416K inode_cache /sys/kernel/slab/skbuff_head_cache/alloc_calls : 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 cpus=0,2,4,18 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 cpus=0,10 /sys/kernel/slab/skbuff_head_cache/free_calls: 13492 age=4295073614 pid=0 cpus=0 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 cpus=1-19 6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 cpus=4,8,10,12,14 3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 pid=0-11605 cpus=5,7,12 1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 cpus=4,12 1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 pid=9915-11581 cpus=8,16,18 2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 pid=11605-11699 cpus=2,9 1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 pid=331 cpus=11 8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] age=8545/62184/110571 pid=11863 cpus=0 By comparison, when running 4.13 with c67df11f reverted, here's the same output after the exact same test: free -h: totalusedfree shared buff/cache available Mem: 39G783M 37G472K637M 37G slabtop: OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 714256 35%0.75K 17 42 544K skbuff_head_cache /sys/kernel/slab/skbuff_head_cache/alloc_calls: 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 /sys/kernel/slab/skbuff_head_cache/free_calls: 255 age=4295003081 pid=0 cpus=0 1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16 Thanks a lot for the test, and sorry for the late update, I was working on the code path and didn't find anything helpful to you till today. I did some tests and initially it turned out that the bottleneck was the guest kernel stack(napi) side, followed by tracking the traffic footprints and it appeared as the loss happened when vring was full and could not be drained out by the guest, afterwards it triggered a SKB drop in vhost driver due to no headcount to fill it with, it can be avoided by deferring consuming the SKB after having obtained a sufficient headcount with below patch. Could you please try it? It is based on 4.13 and I also applied Jason's 'conditionally enable tx polling' patch. https://lkml.org/lkml/2016/6/1/39 This patch has already been merged. I only tested one instance case from Host -> VM with uperf & iperf3, I like iperf3 a bit more since it spontaneously tells the retransmitted and cwnd during testing. :) To maximize the performance of one instance case, two vcpus are needed, one does the kernel napi and the other one should serve the socket syscall (mostly reading) from uperf/iperf userspace, so I set two vcpus to the guest and p
Re: Regression in throughput between kvm guests over virtual bridge
On Mon, Nov 20, 2017 at 02:25:17PM -0500, Matthew Rosato wrote: > On 11/14/2017 03:11 PM, Matthew Rosato wrote: > > On 11/12/2017 01:34 PM, Wei Xu wrote: > >> On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: > > This case should be quite similar with pkgten, if you got improvement > > with > > pktgen, usually it was also the same for UDP, could you please try to > > disable > > tso, gso, gro, ufo on all host tap devices and guest virtio-net > > devices? Currently > > the most significant tests would be like this AFAICT: > > > > Host->VM 4.124.13 > > TCP: > > UDP: > > pktgen: > > So, I automated these scenarios for extended overnight runs and started > experiencing OOM conditions overnight on a 40G system. I did a bisect > and it also points to c67df11f. I can see a leak in at least all of the > Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the > fastest leak. > > I enabled slub_debug on base 4.13 and ran my pktgen scenario in short > intervals until a large% of host memory was consumed. Numbers below > after the last pktgen run completed. The summary is that a very large # > of active skbuff_head_cache entries can be seen - The sum of alloc/free > calls match up, but the # of active skbuff_head_cache entries keeps > growing each time the workload is run and never goes back down in > between runs. > > free -h: > totalusedfree shared buff/cache available > Mem: 39G 31G6.6G472K1.4G6.8G > > OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > 1001952 1000610 99%0.75K 23856 42763392K skbuff_head_cache > 126192 126153 99%0.36K 2868 44 45888K ksm_rmap_item > 100485 100435 99%0.41K 1305 77 41760K kernfs_node_cache > 63294 39598 62%0.48K959 66 30688K dentry > 31968 31719 99%0.88K888 36 28416K inode_cache > > /sys/kernel/slab/skbuff_head_cache/alloc_calls : > 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 cpus=0,2,4,18 > 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 cpus=0,10 > > /sys/kernel/slab/skbuff_head_cache/free_calls: > 13492 age=4295073614 pid=0 cpus=0 > 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 > cpus=1-19 > 6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 > cpus=4,8,10,12,14 > 3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 > pid=0-11605 cpus=5,7,12 > 1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 > 2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 cpus=4,12 > 1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 > 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 > 3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 > pid=9915-11581 cpus=8,16,18 > 2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 > pid=11605-11699 cpus=2,9 > 1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 > pid=331 cpus=11 >8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] age=8545/62184/110571 > pid=11863 cpus=0 > > > By comparison, when running 4.13 with c67df11f reverted, here's the same > output after the exact same test: > > free -h: >totalusedfree shared buff/cache available > Mem: 39G783M 37G472K637M 37G > > slabtop: > OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME >714256 35%0.75K 17 42 544K skbuff_head_cache > > /sys/kernel/slab/skbuff_head_cache/alloc_calls: > 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 > /sys/kernel/slab/skbuff_head_cache/free_calls: > 255 age=4295003081 pid=0 cpus=0 > 1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 > 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16 > Thanks a lot for the test, and sorry for the late update, I was working on the code path and didn't find anything helpful to you till today. I did some tests and initially it turned out that the bottleneck was the guest kernel stack(napi) side, followed by tracking the traffic footprints and it appeared as the loss happened when vring was full and could not be drained out by the guest, afterwards it triggered a SKB drop in vhost driver due to no headcount to fill it with, it can be avoided by deferring consuming the SKB after having obtained a sufficient headcount with below patch. Could you please try it? It is based on 4.13 and I also applied Jason's 'conditionally enable tx polling' patch. https://lkml.org/lkml/2016/6/1/39 I only tested one instance case from Host -> VM with uperf & iperf3, I like iperf3 a bit more since it spontaneously tells the retransmitted and cwnd during testing. :) To maximize the performance of one instance case, two vcpus are needed, one does the kernel napi an
Re: Regression in throughput between kvm guests over virtual bridge
On 11/14/2017 03:11 PM, Matthew Rosato wrote: > On 11/12/2017 01:34 PM, Wei Xu wrote: >> On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: > This case should be quite similar with pkgten, if you got improvement with > pktgen, usually it was also the same for UDP, could you please try to > disable > tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? > Currently > the most significant tests would be like this AFAICT: > > Host->VM 4.124.13 > TCP: > UDP: > pktgen: So, I automated these scenarios for extended overnight runs and started experiencing OOM conditions overnight on a 40G system. I did a bisect and it also points to c67df11f. I can see a leak in at least all of the Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the fastest leak. I enabled slub_debug on base 4.13 and ran my pktgen scenario in short intervals until a large% of host memory was consumed. Numbers below after the last pktgen run completed. The summary is that a very large # of active skbuff_head_cache entries can be seen - The sum of alloc/free calls match up, but the # of active skbuff_head_cache entries keeps growing each time the workload is run and never goes back down in between runs. free -h: totalusedfree shared buff/cache available Mem: 39G 31G6.6G472K1.4G6.8G OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 1001952 1000610 99%0.75K 23856 42763392K skbuff_head_cache 126192 126153 99%0.36K 2868 44 45888K ksm_rmap_item 100485 100435 99%0.41K 1305 77 41760K kernfs_node_cache 63294 39598 62%0.48K959 66 30688K dentry 31968 31719 99%0.88K888 36 28416K inode_cache /sys/kernel/slab/skbuff_head_cache/alloc_calls : 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 cpus=0,2,4,18 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 cpus=0,10 /sys/kernel/slab/skbuff_head_cache/free_calls: 13492 age=4295073614 pid=0 cpus=0 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 cpus=1-19 6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 cpus=4,8,10,12,14 3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 pid=0-11605 cpus=5,7,12 1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 cpus=4,12 1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 pid=9915-11581 cpus=8,16,18 2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 pid=11605-11699 cpus=2,9 1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 pid=331 cpus=11 8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] age=8545/62184/110571 pid=11863 cpus=0 By comparison, when running 4.13 with c67df11f reverted, here's the same output after the exact same test: free -h: totalusedfree shared buff/cache available Mem: 39G783M 37G472K637M 37G slabtop: OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 714256 35%0.75K 17 42 544K skbuff_head_cache /sys/kernel/slab/skbuff_head_cache/alloc_calls: 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 /sys/kernel/slab/skbuff_head_cache/free_calls: 255 age=4295003081 pid=0 cpus=0 1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16
Re: Regression in throughput between kvm guests over virtual bridge
On 11/12/2017 01:34 PM, Wei Xu wrote: > On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: This case should be quite similar with pkgten, if you got improvement with pktgen, usually it was also the same for UDP, could you please try to disable tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? Currently the most significant tests would be like this AFAICT: Host->VM 4.124.13 TCP: UDP: pktgen: Don't want to bother you too much, so maybe 4.12 & 4.13 without Jason's patch should work since we have seen positive number for that, you can also temporarily skip net-next as well. >>> >>> Here are the requested numbers, averaged over numerous runs -- guest is >>> 4GB+1vcpu, host uperf/pktgen bound to 1 host CPU + qemu and vhost thread >>> pinned to other unique host CPUs. tso, gso, gro, ufo disabled on host >>> taps / guest virtio-net devs as requested: >>> >>> Host->VM4.124.13 >>> TCP:9.92Gb/s6.44Gb/s >>> UDP:5.77Gb/s6.63Gb/s >>> pktgen: 1572403pps 1904265pps >>> >>> UDP/pktgen both show improvement from 4.12->4.13. More interesting, >>> however, is that I am seeing the TCP regression for the first time from >>> host->VM. I wonder if the combination of CPU binding + disabling of one >>> or more of tso/gso/gro/ufo is related. >>> If you see UDP and pktgen are aligned, then it might be helpful to continue the other two cases, otherwise we fail in the first place. >>> >> >> I continued running many iterations of these tests between 4.12 and >> 4.13.. My throughput findings can be summarized as: > > Really nice to have these numbers. > Wasn't sure if you were asking for the individual #s -- Just in case, here are the other averages I used to draw my conclusions: VM->VM 4.124.13 UDP 9.06Gb/s8.99Gb/s TCP 9.16Gb/s8.67Gb/s VM->Host4.124.13 UDP 9.70Gb/s9.53Gb/s TCP 6.12Gb/s6.00Gb/s >> >> VM->VM case: >> UDP: roughly equivalent >> TCP: Consistent regression (5-10%) >> >> VM->Host >> Both UDP and TCP traffic are roughly equivalent. > > The patch improves performance for Rx from guest point of view, so the Tx > would be no big difference since the Rx packets are far less than Tx in > this case. > >> >> Host->VM >> UDP+pktgen: improvement (5-10%), but inconsistent >> TCP: Consistent regression (25-30%) > > Maybe we can try to figure out this case first since it is the shortest path, > can you have a look at TCP statistics and paste a few outputs between tests? > I am suspecting there are some retransmitting, zero window probing, etc. > Grabbed some netperf -s results after a few minutes of running (snipped uninteresting icmp and udp sections). The test was TCP Host->VM scenario, binding and tso/gso/gro/ufo disabled as before: Host 4.12 Ip: Forwarding: 1 3724964 total packets received 0 forwarded 0 incoming packets discarded 3724964 incoming packets delivered 526 requests sent out Tcp: 4 active connection openings 1 passive connection openings 0 failed connection attempts 0 connection resets received 1 connections established 3724954 segments received 133112205 segments sent out 93106 segments retransmitted 0 bad segments received 2 resets sent TcpExt: 5 delayed acks sent 8 packets directly queued to recvmsg prequeue TCPDirectCopyFromPrequeue: 1736 146 packet headers predicted 4 packet headers predicted and directly queued to user 3218205 acknowledgments not containing data payload received 506561 predicted acknowledgments TCPSackRecovery: 2096 TCPLostRetransmit: 860 93106 fast retransmits TCPLossProbes: 5 TCPSackShifted: 1959097 TCPSackMerged: 458343 TCPSackShiftFallback: 7969 TCPRcvCoalesce: 2 TCPOrigDataSent: 133112178 TCPHystartTrainDetect: 2 TCPHystartTrainCwnd: 96 TCPWinProbe: 2 IpExt: InBcastPkts: 4 InOctets: 226014831 OutOctets: 193103919403 InBcastOctets: 1312 InNoECTPkts: 3724964 Host 4.13 Ip: Forwarding: 1 5930785 total packets received 0 forwarded 0 incoming packets discarded 5930785 incoming packets delivered 4495113 requests sent out Tcp: 4 active connection openings 1 passive connection openings 0 failed connection attempts 0 connection resets received 1 connections established 5930775 segments received 73226521 segments sent out 13975 segments retransmitted 0 bad segments received 4 resets sent TcpExt: 5 delayed acks sent 8 packets directly queued to recvmsg prequeue TCPDirectCopyFromPrequeue: 1736 18 packet headers predicted 4 packet headers predicted and directly queued to user 4091720 acknowle
Re: Regression in throughput between kvm guests over virtual bridge
On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: > >> This case should be quite similar with pkgten, if you got improvement with > >> pktgen, usually it was also the same for UDP, could you please try to > >> disable > >> tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? > >> Currently > >> the most significant tests would be like this AFAICT: > >> > >> Host->VM 4.124.13 > >> TCP: > >> UDP: > >> pktgen: > >> > >> Don't want to bother you too much, so maybe 4.12 & 4.13 without Jason's > >> patch should > >> work since we have seen positive number for that, you can also temporarily > >> skip > >> net-next as well. > > > > Here are the requested numbers, averaged over numerous runs -- guest is > > 4GB+1vcpu, host uperf/pktgen bound to 1 host CPU + qemu and vhost thread > > pinned to other unique host CPUs. tso, gso, gro, ufo disabled on host > > taps / guest virtio-net devs as requested: > > > > Host->VM4.124.13 > > TCP:9.92Gb/s6.44Gb/s > > UDP:5.77Gb/s6.63Gb/s > > pktgen: 1572403pps 1904265pps > > > > UDP/pktgen both show improvement from 4.12->4.13. More interesting, > > however, is that I am seeing the TCP regression for the first time from > > host->VM. I wonder if the combination of CPU binding + disabling of one > > or more of tso/gso/gro/ufo is related. > > > >> > >> If you see UDP and pktgen are aligned, then it might be helpful to continue > >> the other two cases, otherwise we fail in the first place. > > > > I continued running many iterations of these tests between 4.12 and > 4.13.. My throughput findings can be summarized as: Really nice to have these numbers. > > VM->VM case: > UDP: roughly equivalent > TCP: Consistent regression (5-10%) > > VM->Host > Both UDP and TCP traffic are roughly equivalent. The patch improves performance for Rx from guest point of view, so the Tx would be no big difference since the Rx packets are far less than Tx in this case. > > Host->VM > UDP+pktgen: improvement (5-10%), but inconsistent > TCP: Consistent regression (25-30%) Maybe we can try to figure out this case first since it is the shortest path, can you have a look at TCP statistics and paste a few outputs between tests? I am suspecting there are some retransmitting, zero window probing, etc. > > Host->VM UDP and pktgen seemed to show improvement in some runs, and in > others seemed to mirror 4.12-level performance. > > The TCP regression for VM->VM is no surprise, we started with that. > It's still consistent, but smaller in this specific environment. Right, there are too many facts might influent the performance. > > The TCP regression in Host->VM is interesting because I wasn't seeing it > consistently before binding CPUs + disabling tso/gso/gro/ufo. Also > interesting because of how large it is -- By any chance can you see this > regression on x86 with the same configuration? Had a quick test and it seems I also got drop on x86 without tso,gro,..., data with/without tso,gso,..., will check out tcp statistics and let you know soon. 4.12 -- master32.34s 112.63GB29.91Gb/s 40310900.00 master32.33s32.58GB 8.66Gb/s 11660140.00 - 4.13 - master32.35s 119.17GB31.64Gb/s 42651900.00 master32.33s27.02GB 7.18Gb/s 9670070.00 - Wei
Re: Regression in throughput between kvm guests over virtual bridge
On Tue, Nov 07, 2017 at 08:02:48PM -0500, Matthew Rosato wrote: > On 11/04/2017 07:35 PM, Wei Xu wrote: > > On Fri, Nov 03, 2017 at 12:30:12AM -0400, Matthew Rosato wrote: > >> On 10/31/2017 03:07 AM, Wei Xu wrote: > >>> On Thu, Oct 26, 2017 at 01:53:12PM -0400, Matthew Rosato wrote: > > > > > Are you using the same binding as mentioned in previous mail sent by > > you? it > > might be caused by cpu convention between pktgen and vhost, could you > > please > > try to run pktgen from another idle cpu by adjusting the binding? > > I don't think that's the case -- I can cause pktgen to hang in the guest > without any cpu binding, and with vhost disabled even. > >>> > >>> Yes, I did a test and it also hangs in guest, before we figure it out, > >>> maybe you try udp with uperf with this case? > >>> > >>> VM -> Host > >>> Host -> VM > >>> VM -> VM > >>> > >> > >> Here are averaged run numbers (Gbps throughput) across 4.12, 4.13 and > >> net-next with and without Jason's recent "vhost_net: conditionally > >> enable tx polling" applied (referred to as 'patch' below). 1 uperf > >> instance in each case: > > > > Thanks a lot for the test. > > > >> > >> uperf TCP: > >> 4.12 4.134.13+patch net-nextnet-next+patch > >> -- > >> VM->VM 35.2 16.520.84 22.224.36 > > > > Are you using the same server/test suite? You mentioned the number was > > around > > 28Gb for 4.12 and it dropped about 40% for 4.13, it seems thing changed, are > > there any options for performance tuning on the server to maximize the cpu > > utilization? > > I experience some volatility as I am running on 1 of multiple LPARs > available to this system (they are sharing physical resources). But I > think the real issue was that I left my guest environment set to 4 > vcpus, but was binding assuming there was 1 vcpu (was working on > something else, forgot to change back). This likely tainted my most > recent results, sorry. Not a problem at all, also thanks for the feedback. :) > > > > > I had similar experience on x86 server and desktop before and it made that > > the result number always went up and down pretty much. > > > >> VM->Host 42.15 43.57 44.90 30.83 32.26 > >> Host->VM 53.17 41.51 42.18 37.05 37.30 > > > > This is a bit odd, I remember you said there was no regression while > > testing Host>VM, wasn't it? > > > >> > >> uperf UDP: > >> 4.12 4.134.13+patch net-nextnet-next+patch > >> -- > >> VM->VM 24.93 21.63 25.09 8.869.62 > >> VM->Host 40.21 38.21 39.72 8.749.35 > >> Host->VM 31.26 30.18 31.25 7.2 9.26 > > > > This case should be quite similar with pkgten, if you got improvement with > > pktgen, usually it was also the same for UDP, could you please try to > > disable > > tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? > > Currently > > the most significant tests would be like this AFAICT: > > > > Host->VM 4.124.13 > > TCP: > > UDP: > > pktgen: > > > > Don't want to bother you too much, so maybe 4.12 & 4.13 without Jason's > > patch should > > work since we have seen positive number for that, you can also temporarily > > skip > > net-next as well. > > Here are the requested numbers, averaged over numerous runs -- guest is > 4GB+1vcpu, host uperf/pktgen bound to 1 host CPU + qemu and vhost thread > pinned to other unique host CPUs. tso, gso, gro, ufo disabled on host > taps / guest virtio-net devs as requested: > > Host->VM 4.124.13 > TCP: 9.92Gb/s6.44Gb/s > UDP: 5.77Gb/s6.63Gb/s > pktgen: 1572403pps 1904265pps > > UDP/pktgen both show improvement from 4.12->4.13. More interesting, > however, is that I am seeing the TCP regression for the first time from > host->VM. I wonder if the combination of CPU binding + disabling of one > or more of tso/gso/gro/ufo is related. Interesting, then maybe we can address the regression based on this case first if we can reproduce it. Can you have a look at TCP statistics difference on both host and guest side with 'netstat -s' between tests? Wei > > > > > If you see UDP and pktgen are aligned, then it might be helpful to continue > > the other two cases, otherwise we fail in the first place. > > I will start gathering those numbers tomorrow. > > > > >> The net is that Jason's recent patch definitely improves things across > >> the board at 4.13 as well as at net-next -- But the VM<->VM TCP numbers > >> I am observing are still lower than base 4.12. > > > > Cool. > > > >> > >> A separate concern is why my UDP numbers look so bad on net-next (have > >> not bisected this
Re: Regression in throughput between kvm guests over virtual bridge
>> This case should be quite similar with pkgten, if you got improvement with >> pktgen, usually it was also the same for UDP, could you please try to disable >> tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? >> Currently >> the most significant tests would be like this AFAICT: >> >> Host->VM 4.124.13 >> TCP: >> UDP: >> pktgen: >> >> Don't want to bother you too much, so maybe 4.12 & 4.13 without Jason's >> patch should >> work since we have seen positive number for that, you can also temporarily >> skip >> net-next as well. > > Here are the requested numbers, averaged over numerous runs -- guest is > 4GB+1vcpu, host uperf/pktgen bound to 1 host CPU + qemu and vhost thread > pinned to other unique host CPUs. tso, gso, gro, ufo disabled on host > taps / guest virtio-net devs as requested: > > Host->VM 4.124.13 > TCP: 9.92Gb/s6.44Gb/s > UDP: 5.77Gb/s6.63Gb/s > pktgen: 1572403pps 1904265pps > > UDP/pktgen both show improvement from 4.12->4.13. More interesting, > however, is that I am seeing the TCP regression for the first time from > host->VM. I wonder if the combination of CPU binding + disabling of one > or more of tso/gso/gro/ufo is related. > >> >> If you see UDP and pktgen are aligned, then it might be helpful to continue >> the other two cases, otherwise we fail in the first place. > I continued running many iterations of these tests between 4.12 and 4.13.. My throughput findings can be summarized as: VM->VM case: UDP: roughly equivalent TCP: Consistent regression (5-10%) VM->Host Both UDP and TCP traffic are roughly equivalent. Host->VM UDP+pktgen: improvement (5-10%), but inconsistent TCP: Consistent regression (25-30%) Host->VM UDP and pktgen seemed to show improvement in some runs, and in others seemed to mirror 4.12-level performance. The TCP regression for VM->VM is no surprise, we started with that. It's still consistent, but smaller in this specific environment. The TCP regression in Host->VM is interesting because I wasn't seeing it consistently before binding CPUs + disabling tso/gso/gro/ufo. Also interesting because of how large it is -- By any chance can you see this regression on x86 with the same configuration?
Re: Regression in throughput between kvm guests over virtual bridge
On 11/04/2017 07:35 PM, Wei Xu wrote: > On Fri, Nov 03, 2017 at 12:30:12AM -0400, Matthew Rosato wrote: >> On 10/31/2017 03:07 AM, Wei Xu wrote: >>> On Thu, Oct 26, 2017 at 01:53:12PM -0400, Matthew Rosato wrote: > > Are you using the same binding as mentioned in previous mail sent by you? > it > might be caused by cpu convention between pktgen and vhost, could you > please > try to run pktgen from another idle cpu by adjusting the binding? I don't think that's the case -- I can cause pktgen to hang in the guest without any cpu binding, and with vhost disabled even. >>> >>> Yes, I did a test and it also hangs in guest, before we figure it out, >>> maybe you try udp with uperf with this case? >>> >>> VM -> Host >>> Host -> VM >>> VM -> VM >>> >> >> Here are averaged run numbers (Gbps throughput) across 4.12, 4.13 and >> net-next with and without Jason's recent "vhost_net: conditionally >> enable tx polling" applied (referred to as 'patch' below). 1 uperf >> instance in each case: > > Thanks a lot for the test. > >> >> uperf TCP: >> 4.12 4.134.13+patch net-nextnet-next+patch >> -- >> VM->VM35.2 16.520.84 22.224.36 > > Are you using the same server/test suite? You mentioned the number was around > 28Gb for 4.12 and it dropped about 40% for 4.13, it seems thing changed, are > there any options for performance tuning on the server to maximize the cpu > utilization? I experience some volatility as I am running on 1 of multiple LPARs available to this system (they are sharing physical resources). But I think the real issue was that I left my guest environment set to 4 vcpus, but was binding assuming there was 1 vcpu (was working on something else, forgot to change back). This likely tainted my most recent results, sorry. > > I had similar experience on x86 server and desktop before and it made that > the result number always went up and down pretty much. > >> VM->Host 42.15 43.57 44.90 30.83 32.26 >> Host->VM 53.17 41.51 42.18 37.05 37.30 > > This is a bit odd, I remember you said there was no regression while > testing Host>VM, wasn't it? > >> >> uperf UDP: >> 4.12 4.134.13+patch net-nextnet-next+patch >> -- >> VM->VM24.93 21.63 25.09 8.869.62 >> VM->Host 40.21 38.21 39.72 8.749.35 >> Host->VM 31.26 30.18 31.25 7.2 9.26 > > This case should be quite similar with pkgten, if you got improvement with > pktgen, usually it was also the same for UDP, could you please try to disable > tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? > Currently > the most significant tests would be like this AFAICT: > > Host->VM 4.124.13 > TCP: > UDP: > pktgen: > > Don't want to bother you too much, so maybe 4.12 & 4.13 without Jason's patch > should > work since we have seen positive number for that, you can also temporarily > skip > net-next as well. Here are the requested numbers, averaged over numerous runs -- guest is 4GB+1vcpu, host uperf/pktgen bound to 1 host CPU + qemu and vhost thread pinned to other unique host CPUs. tso, gso, gro, ufo disabled on host taps / guest virtio-net devs as requested: Host->VM4.124.13 TCP:9.92Gb/s6.44Gb/s UDP:5.77Gb/s6.63Gb/s pktgen: 1572403pps 1904265pps UDP/pktgen both show improvement from 4.12->4.13. More interesting, however, is that I am seeing the TCP regression for the first time from host->VM. I wonder if the combination of CPU binding + disabling of one or more of tso/gso/gro/ufo is related. > > If you see UDP and pktgen are aligned, then it might be helpful to continue > the other two cases, otherwise we fail in the first place. I will start gathering those numbers tomorrow. > >> The net is that Jason's recent patch definitely improves things across >> the board at 4.13 as well as at net-next -- But the VM<->VM TCP numbers >> I am observing are still lower than base 4.12. > > Cool. > >> >> A separate concern is why my UDP numbers look so bad on net-next (have >> not bisected this yet). > > This might be another issue, I am in vacation, will try it on x86 once back > to work on next Wednesday. > > Wei > >> >
Re: Regression in throughput between kvm guests over virtual bridge
On Fri, Nov 03, 2017 at 12:30:12AM -0400, Matthew Rosato wrote: > On 10/31/2017 03:07 AM, Wei Xu wrote: > > On Thu, Oct 26, 2017 at 01:53:12PM -0400, Matthew Rosato wrote: > >> > >>> > >>> Are you using the same binding as mentioned in previous mail sent by you? > >>> it > >>> might be caused by cpu convention between pktgen and vhost, could you > >>> please > >>> try to run pktgen from another idle cpu by adjusting the binding? > >> > >> I don't think that's the case -- I can cause pktgen to hang in the guest > >> without any cpu binding, and with vhost disabled even. > > > > Yes, I did a test and it also hangs in guest, before we figure it out, > > maybe you try udp with uperf with this case? > > > > VM -> Host > > Host -> VM > > VM -> VM > > > > Here are averaged run numbers (Gbps throughput) across 4.12, 4.13 and > net-next with and without Jason's recent "vhost_net: conditionally > enable tx polling" applied (referred to as 'patch' below). 1 uperf > instance in each case: Thanks a lot for the test. > > uperf TCP: >4.12 4.134.13+patch net-nextnet-next+patch > -- > VM->VM 35.2 16.520.84 22.224.36 Are you using the same server/test suite? You mentioned the number was around 28Gb for 4.12 and it dropped about 40% for 4.13, it seems thing changed, are there any options for performance tuning on the server to maximize the cpu utilization? I had similar experience on x86 server and desktop before and it made that the result number always went up and down pretty much. > VM->Host 42.1543.57 44.90 30.83 32.26 > Host->VM 53.1741.51 42.18 37.05 37.30 This is a bit odd, I remember you said there was no regression while testing Host>VM, wasn't it? > > uperf UDP: >4.12 4.134.13+patch net-nextnet-next+patch > -- > VM->VM 24.93 21.63 25.09 8.869.62 > VM->Host 40.2138.21 39.72 8.749.35 > Host->VM 31.2630.18 31.25 7.2 9.26 This case should be quite similar with pkgten, if you got improvement with pktgen, usually it was also the same for UDP, could you please try to disable tso, gso, gro, ufo on all host tap devices and guest virtio-net devices? Currently the most significant tests would be like this AFAICT: Host->VM 4.124.13 TCP: UDP: pktgen: Don't want to bother you too much, so maybe 4.12 & 4.13 without Jason's patch should work since we have seen positive number for that, you can also temporarily skip net-next as well. If you see UDP and pktgen are aligned, then it might be helpful to continue the other two cases, otherwise we fail in the first place. > The net is that Jason's recent patch definitely improves things across > the board at 4.13 as well as at net-next -- But the VM<->VM TCP numbers > I am observing are still lower than base 4.12. Cool. > > A separate concern is why my UDP numbers look so bad on net-next (have > not bisected this yet). This might be another issue, I am in vacation, will try it on x86 once back to work on next Wednesday. Wei >
Re: Regression in throughput between kvm guests over virtual bridge
On 10/31/2017 03:07 AM, Wei Xu wrote: > On Thu, Oct 26, 2017 at 01:53:12PM -0400, Matthew Rosato wrote: >> >>> >>> Are you using the same binding as mentioned in previous mail sent by you? it >>> might be caused by cpu convention between pktgen and vhost, could you please >>> try to run pktgen from another idle cpu by adjusting the binding? >> >> I don't think that's the case -- I can cause pktgen to hang in the guest >> without any cpu binding, and with vhost disabled even. > > Yes, I did a test and it also hangs in guest, before we figure it out, > maybe you try udp with uperf with this case? > > VM -> Host > Host -> VM > VM -> VM > Here are averaged run numbers (Gbps throughput) across 4.12, 4.13 and net-next with and without Jason's recent "vhost_net: conditionally enable tx polling" applied (referred to as 'patch' below). 1 uperf instance in each case: uperf TCP: 4.12 4.134.13+patch net-nextnet-next+patch -- VM->VM 35.2 16.520.84 22.224.36 VM->Host 42.15 43.57 44.90 30.83 32.26 Host->VM 53.17 41.51 42.18 37.05 37.30 uperf UDP: 4.12 4.134.13+patch net-nextnet-next+patch -- VM->VM 24.93 21.63 25.09 8.869.62 VM->Host 40.21 38.21 39.72 8.749.35 Host->VM 31.26 30.18 31.25 7.2 9.26 The net is that Jason's recent patch definitely improves things across the board at 4.13 as well as at net-next -- But the VM<->VM TCP numbers I am observing are still lower than base 4.12. A separate concern is why my UDP numbers look so bad on net-next (have not bisected this yet).
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年10月31日 15:07, Wei Xu wrote: BTW, did you see any improvement when running pktgen from the host if no regression was found? Since this can be reproduced with only 1 vcpu for guest, may you try this bind? This might help simplify the problem. vcpu0 -> cpu2 vhost -> cpu3 pktgen -> cpu1 Yes -- I ran the pktgen test from host to guest with the binding described. I see an approx 5% increase in throughput from 4.12->4.13. Some numbers: host-4.12: 1384486.2pps 663.8MB/sec host-4.13: 1434598.6pps 688.2MB/sec That's great, at least we are aligned in this case. Jason, any thoughts on this? Wei Good news is that pps is increased. I think the first step is moving things a little bit ahead by reposting the optimization of tx polling. I will post a new version soon. Thanks
Re: Regression in throughput between kvm guests over virtual bridge
On Thu, Oct 26, 2017 at 01:53:12PM -0400, Matthew Rosato wrote: > > > > > Are you using the same binding as mentioned in previous mail sent by you? it > > might be caused by cpu convention between pktgen and vhost, could you please > > try to run pktgen from another idle cpu by adjusting the binding? > > I don't think that's the case -- I can cause pktgen to hang in the guest > without any cpu binding, and with vhost disabled even. Yes, I did a test and it also hangs in guest, before we figure it out, maybe you try udp with uperf with this case? VM -> Host Host -> VM VM -> VM > > > BTW, did you see any improvement when running pktgen from the host if no > > regression was found? Since this can be reproduced with only 1 vcpu for > > guest, may you try this bind? This might help simplify the problem. > > vcpu0 -> cpu2 > > vhost -> cpu3 > > pktgen -> cpu1 > > > > Yes -- I ran the pktgen test from host to guest with the binding > described. I see an approx 5% increase in throughput from 4.12->4.13. > Some numbers: > > host-4.12: 1384486.2pps 663.8MB/sec > host-4.13: 1434598.6pps 688.2MB/sec That's great, at least we are aligned in this case. Jason, any thoughts on this? Wei >
Re: Regression in throughput between kvm guests over virtual bridge
> > Are you using the same binding as mentioned in previous mail sent by you? it > might be caused by cpu convention between pktgen and vhost, could you please > try to run pktgen from another idle cpu by adjusting the binding? I don't think that's the case -- I can cause pktgen to hang in the guest without any cpu binding, and with vhost disabled even. > BTW, did you see any improvement when running pktgen from the host if no > regression was found? Since this can be reproduced with only 1 vcpu for > guest, may you try this bind? This might help simplify the problem. > vcpu0 -> cpu2 > vhost -> cpu3 > pktgen -> cpu1 > Yes -- I ran the pktgen test from host to guest with the binding described. I see an approx 5% increase in throughput from 4.12->4.13. Some numbers: host-4.12: 1384486.2pps 663.8MB/sec host-4.13: 1434598.6pps 688.2MB/sec
Re: Regression in throughput between kvm guests over virtual bridge
On Wed, Oct 25, 2017 at 04:21:26PM -0400, Matthew Rosato wrote: > On 10/22/2017 10:06 PM, Jason Wang wrote: > > > > > > On 2017年10月19日 04:17, Matthew Rosato wrote: > >>> 2. It might be useful to short the traffic path as a reference, What > >>> I am running > >>> is briefly like: > >>> pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) > >>> > >>> The bridge driver(br_forward(), etc) might impact performance due to > >>> my personal > >>> experience, so eventually I settled down with this simplified testbed > >>> which fully > >>> isolates the traffic from both userspace and host kernel stack(1 and > >>> 50 instances, > >>> bridge driver, etc), therefore reduces potential interferences. > >>> > >>> The down side of this is that it needs DPDK support in guest, has > >>> this ever be > >>> run on s390x guest? An alternative approach is to directly run XDP > >>> drop on > >>> virtio-net nic in guest, while this requires compiling XDP inside > >>> guest which needs > >>> a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). > >>> > >> I made an attempt at DPDK, but it has not been run on s390x as far as > >> I'm aware and didn't seem trivial to get working. > >> > >> So instead I took your alternate suggestion & did: > >> pktgen(host) -> tap(x) -> guest(xdp_drop) > >> > >> When running this setup, I am not able to reproduce the regression. As > >> mentioned previously, I am also unable to reproduce when running one end > >> of the uperf connection from the host - I have only ever been able to > >> reproduce when both ends of the uperf connection are running within a > >> guest. > >> > > > > Thanks for the test. Looking at the code, the only obvious difference > > when BATCH is 1 is that one spinlock which was previously called by > > tun_peek_len() was avoided since we can do it locally. I wonder whether > > or not this speeds up handle_rx() a little more then leads more wakeups > > during some rates/sizes of TCP stream. To prove this, maybe you can try: > > > > - enable busy polling, using poll-us=1000, and to see if we can still > > get the regression > > Enabled poll-us=1000 for both guests - drastically reduces throughput, > but can still see the regression between host 4.12->4.13 running the > uperf workload > > > > - measure the pps pktgen(vm1) -> tap1 -> bridge -> tap2 -> vm2 > > > > I'm getting apparent stalls when I run pktgen from the guest in this > manner... (pktgen thread continues spinning after the first 5000 > packets make it to vm2, but no further packets get sent). Not sure why yet. > Are you using the same binding as mentioned in previous mail sent by you? it might be caused by cpu convention between pktgen and vhost, could you please try to run pktgen from another idle cpu by adjusting the binding? BTW, did you see any improvement when running pktgen from the host if no regression was found? Since this can be reproduced with only 1 vcpu for guest, may you try this bind? This might help simplify the problem. vcpu0 -> cpu2 vhost -> cpu3 pktgen -> cpu1 Wei
Re: Regression in throughput between kvm guests over virtual bridge
On 10/23/2017 09:57 AM, Wei Xu wrote: > On Wed, Oct 18, 2017 at 04:17:51PM -0400, Matthew Rosato wrote: >> On 10/12/2017 02:31 PM, Wei Xu wrote: >>> On Thu, Oct 05, 2017 at 04:07:45PM -0400, Matthew Rosato wrote: Ping... Jason, any other ideas or suggestions? >>> >>> Hi Matthew, >>> Recently I am doing similar test on x86 for this patch, here are some, >>> differences between our testbeds. >>> >>> 1. It is nice you have got improvement with 50+ instances(or connections >>> here?) >>> which would be quite helpful to address the issue, also you've figured out >>> the >>> cost(wait/wakeup), kindly reminder did you pin uperf client/server along >>> the whole >>> path besides vhost and vcpu threads? >> >> Was not previously doing any pinning whatsoever, just reproducing an >> environment that one of our testers here was running. Reducing guest >> vcpu count from 4->1, still see the regression. Then, pinned each vcpu >> thread and vhost thread to a separate host CPU -- still made no >> difference (regression still present). >> >>> >>> 2. It might be useful to short the traffic path as a reference, What I am >>> running >>> is briefly like: >>> pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) >>> >>> The bridge driver(br_forward(), etc) might impact performance due to my >>> personal >>> experience, so eventually I settled down with this simplified testbed which >>> fully >>> isolates the traffic from both userspace and host kernel stack(1 and 50 >>> instances, >>> bridge driver, etc), therefore reduces potential interferences. >>> >>> The down side of this is that it needs DPDK support in guest, has this ever >>> be >>> run on s390x guest? An alternative approach is to directly run XDP drop on >>> virtio-net nic in guest, while this requires compiling XDP inside guest >>> which needs >>> a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). >>> >> >> I made an attempt at DPDK, but it has not been run on s390x as far as >> I'm aware and didn't seem trivial to get working. >> >> So instead I took your alternate suggestion & did: >> pktgen(host) -> tap(x) -> guest(xdp_drop) > > It is really nice of you for having tried this, I also tried this on x86 with > two ubuntu 16.04 guests, but unfortunately I couldn't reproduce it as well, > but I did get lower throughput with 50 instances than one instance(1-4 vcpus), > is this the same on s390x? For me, the total throughput is higher from 50 instances than for 1 instance when host kernel is 4.13. However, when running a 50 instance uperf load I cannot reproduce the regression, either. Throughput is a little bit better when host is 4.13 vs 4.12 for a 50 instance run. > >> >> When running this setup, I am not able to reproduce the regression. As >> mentioned previously, I am also unable to reproduce when running one end >> of the uperf connection from the host - I have only ever been able to >> reproduce when both ends of the uperf connection are running within a guest. > > Did you see improvement when running uperf from the host if no regression? > > It would be pretty nice to run pktgen from the VM as Jason suggested in > another > mail(pktgen(vm1) -> tap1 -> bridge -> tap2 -> vm2), this is super close to > your > original test case and can help to determine if we can get some clue with tcp > or > bridge driver. > > Also I am interested in your hardware platform, how many NUMA nodes do you > have? > what about your binding(vcpu/vhost/pktgen). For my case, I got a server with 4 > NUMA nodes and 12 cpus for each sockets, and I am explicitly launching qemu > from > cpu0, then bind vhost(Rx/Tx) to cpu 2&3, and vcpus start from cpu 4(3 vcpus > for > each). I'm running in an LPAR on a z13. The particular LPAR I am using to reproduce has 20 CPUs and 40G of memory assigned, all in 1 NUMA node. I was initially recreating an issue uncovered by someone elses test, and thus was doing no cpu binding -- But have attempted binding vhost and vcpu threads to individual host CPUs and it seemed to have no impact on the noted regression. When doing said binding, I did: qemu-guestA -> cpu0(or 0-3 when running 4vcpu), qemu-guestA-vhost -> cpu4, qemu-guestB -> cpu8(or 8-11 when running 4vcpu), qemu-guestB-vhost -> cpu12.
Re: Regression in throughput between kvm guests over virtual bridge
On 10/22/2017 10:06 PM, Jason Wang wrote: > > > On 2017年10月19日 04:17, Matthew Rosato wrote: >>> 2. It might be useful to short the traffic path as a reference, What >>> I am running >>> is briefly like: >>> pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) >>> >>> The bridge driver(br_forward(), etc) might impact performance due to >>> my personal >>> experience, so eventually I settled down with this simplified testbed >>> which fully >>> isolates the traffic from both userspace and host kernel stack(1 and >>> 50 instances, >>> bridge driver, etc), therefore reduces potential interferences. >>> >>> The down side of this is that it needs DPDK support in guest, has >>> this ever be >>> run on s390x guest? An alternative approach is to directly run XDP >>> drop on >>> virtio-net nic in guest, while this requires compiling XDP inside >>> guest which needs >>> a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). >>> >> I made an attempt at DPDK, but it has not been run on s390x as far as >> I'm aware and didn't seem trivial to get working. >> >> So instead I took your alternate suggestion & did: >> pktgen(host) -> tap(x) -> guest(xdp_drop) >> >> When running this setup, I am not able to reproduce the regression. As >> mentioned previously, I am also unable to reproduce when running one end >> of the uperf connection from the host - I have only ever been able to >> reproduce when both ends of the uperf connection are running within a >> guest. >> > > Thanks for the test. Looking at the code, the only obvious difference > when BATCH is 1 is that one spinlock which was previously called by > tun_peek_len() was avoided since we can do it locally. I wonder whether > or not this speeds up handle_rx() a little more then leads more wakeups > during some rates/sizes of TCP stream. To prove this, maybe you can try: > > - enable busy polling, using poll-us=1000, and to see if we can still > get the regression Enabled poll-us=1000 for both guests - drastically reduces throughput, but can still see the regression between host 4.12->4.13 running the uperf workload > - measure the pps pktgen(vm1) -> tap1 -> bridge -> tap2 -> vm2 > I'm getting apparent stalls when I run pktgen from the guest in this manner... (pktgen thread continues spinning after the first 5000 packets make it to vm2, but no further packets get sent). Not sure why yet.
Re: Regression in throughput between kvm guests over virtual bridge
On Wed, Oct 18, 2017 at 04:17:51PM -0400, Matthew Rosato wrote: > On 10/12/2017 02:31 PM, Wei Xu wrote: > > On Thu, Oct 05, 2017 at 04:07:45PM -0400, Matthew Rosato wrote: > >> > >> Ping... Jason, any other ideas or suggestions? > > > > Hi Matthew, > > Recently I am doing similar test on x86 for this patch, here are some, > > differences between our testbeds. > > > > 1. It is nice you have got improvement with 50+ instances(or connections > > here?) > > which would be quite helpful to address the issue, also you've figured out > > the > > cost(wait/wakeup), kindly reminder did you pin uperf client/server along > > the whole > > path besides vhost and vcpu threads? > > Was not previously doing any pinning whatsoever, just reproducing an > environment that one of our testers here was running. Reducing guest > vcpu count from 4->1, still see the regression. Then, pinned each vcpu > thread and vhost thread to a separate host CPU -- still made no > difference (regression still present). > > > > > 2. It might be useful to short the traffic path as a reference, What I am > > running > > is briefly like: > > pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) > > > > The bridge driver(br_forward(), etc) might impact performance due to my > > personal > > experience, so eventually I settled down with this simplified testbed which > > fully > > isolates the traffic from both userspace and host kernel stack(1 and 50 > > instances, > > bridge driver, etc), therefore reduces potential interferences. > > > > The down side of this is that it needs DPDK support in guest, has this ever > > be > > run on s390x guest? An alternative approach is to directly run XDP drop on > > virtio-net nic in guest, while this requires compiling XDP inside guest > > which needs > > a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). > > > > I made an attempt at DPDK, but it has not been run on s390x as far as > I'm aware and didn't seem trivial to get working. > > So instead I took your alternate suggestion & did: > pktgen(host) -> tap(x) -> guest(xdp_drop) It is really nice of you for having tried this, I also tried this on x86 with two ubuntu 16.04 guests, but unfortunately I couldn't reproduce it as well, but I did get lower throughput with 50 instances than one instance(1-4 vcpus), is this the same on s390x? > > When running this setup, I am not able to reproduce the regression. As > mentioned previously, I am also unable to reproduce when running one end > of the uperf connection from the host - I have only ever been able to > reproduce when both ends of the uperf connection are running within a guest. Did you see improvement when running uperf from the host if no regression? It would be pretty nice to run pktgen from the VM as Jason suggested in another mail(pktgen(vm1) -> tap1 -> bridge -> tap2 -> vm2), this is super close to your original test case and can help to determine if we can get some clue with tcp or bridge driver. Also I am interested in your hardware platform, how many NUMA nodes do you have? what about your binding(vcpu/vhost/pktgen). For my case, I got a server with 4 NUMA nodes and 12 cpus for each sockets, and I am explicitly launching qemu from cpu0, then bind vhost(Rx/Tx) to cpu 2&3, and vcpus start from cpu 4(3 vcpus for each). > > > 3. BTW, did you enable hugepage for your guest? It would performance more > > or less depends on the memory demand when generating traffic, I didn't see > > similar command lines in yours. > > > > s390x does not currently support passing through hugetlb backing via > QEMU mem-path. Okay, thanks for sharing this. Wei >
Re: Regression in throughput between kvm guests over virtual bridge
On Mon, Oct 23, 2017 at 10:06:36AM +0800, Jason Wang wrote: > > > On 2017年10月19日 04:17, Matthew Rosato wrote: > > > 2. It might be useful to short the traffic path as a reference, What I am > > > running > > > is briefly like: > > > pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) > > > > > > The bridge driver(br_forward(), etc) might impact performance due to my > > > personal > > > experience, so eventually I settled down with this simplified testbed > > > which fully > > > isolates the traffic from both userspace and host kernel stack(1 and 50 > > > instances, > > > bridge driver, etc), therefore reduces potential interferences. > > > > > > The down side of this is that it needs DPDK support in guest, has this > > > ever be > > > run on s390x guest? An alternative approach is to directly run XDP drop on > > > virtio-net nic in guest, while this requires compiling XDP inside guest > > > which needs > > > a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). > > > > > I made an attempt at DPDK, but it has not been run on s390x as far as > > I'm aware and didn't seem trivial to get working. > > > > So instead I took your alternate suggestion & did: > > pktgen(host) -> tap(x) -> guest(xdp_drop) > > > > When running this setup, I am not able to reproduce the regression. As > > mentioned previously, I am also unable to reproduce when running one end > > of the uperf connection from the host - I have only ever been able to > > reproduce when both ends of the uperf connection are running within a guest. > > > > Thanks for the test. Looking at the code, the only obvious difference when > BATCH is 1 is that one spinlock which was previously called by > tun_peek_len() was avoided since we can do it locally. I wonder whether or > not this speeds up handle_rx() a little more then leads more wakeups during > some rates/sizes of TCP stream. To prove this, maybe you can try: > > - enable busy polling, using poll-us=1000, and to see if we can still get > the regression > - measure the pps pktgen(vm1) -> tap1 -> bridge -> tap2 -> vm2 > > Michael, any another possibility in your mind? > > Thanks Not really. I still suspect since it's s390 only there's some kind of race condition where we wake up a task repeatedly. -- MST
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年10月19日 04:17, Matthew Rosato wrote: 2. It might be useful to short the traffic path as a reference, What I am running is briefly like: pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) The bridge driver(br_forward(), etc) might impact performance due to my personal experience, so eventually I settled down with this simplified testbed which fully isolates the traffic from both userspace and host kernel stack(1 and 50 instances, bridge driver, etc), therefore reduces potential interferences. The down side of this is that it needs DPDK support in guest, has this ever be run on s390x guest? An alternative approach is to directly run XDP drop on virtio-net nic in guest, while this requires compiling XDP inside guest which needs a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). I made an attempt at DPDK, but it has not been run on s390x as far as I'm aware and didn't seem trivial to get working. So instead I took your alternate suggestion & did: pktgen(host) -> tap(x) -> guest(xdp_drop) When running this setup, I am not able to reproduce the regression. As mentioned previously, I am also unable to reproduce when running one end of the uperf connection from the host - I have only ever been able to reproduce when both ends of the uperf connection are running within a guest. Thanks for the test. Looking at the code, the only obvious difference when BATCH is 1 is that one spinlock which was previously called by tun_peek_len() was avoided since we can do it locally. I wonder whether or not this speeds up handle_rx() a little more then leads more wakeups during some rates/sizes of TCP stream. To prove this, maybe you can try: - enable busy polling, using poll-us=1000, and to see if we can still get the regression - measure the pps pktgen(vm1) -> tap1 -> bridge -> tap2 -> vm2 Michael, any another possibility in your mind? Thanks
Re: Regression in throughput between kvm guests over virtual bridge
On 10/12/2017 02:31 PM, Wei Xu wrote: > On Thu, Oct 05, 2017 at 04:07:45PM -0400, Matthew Rosato wrote: >> >> Ping... Jason, any other ideas or suggestions? > > Hi Matthew, > Recently I am doing similar test on x86 for this patch, here are some, > differences between our testbeds. > > 1. It is nice you have got improvement with 50+ instances(or connections > here?) > which would be quite helpful to address the issue, also you've figured out the > cost(wait/wakeup), kindly reminder did you pin uperf client/server along the > whole > path besides vhost and vcpu threads? Was not previously doing any pinning whatsoever, just reproducing an environment that one of our testers here was running. Reducing guest vcpu count from 4->1, still see the regression. Then, pinned each vcpu thread and vhost thread to a separate host CPU -- still made no difference (regression still present). > > 2. It might be useful to short the traffic path as a reference, What I am > running > is briefly like: > pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) > > The bridge driver(br_forward(), etc) might impact performance due to my > personal > experience, so eventually I settled down with this simplified testbed which > fully > isolates the traffic from both userspace and host kernel stack(1 and 50 > instances, > bridge driver, etc), therefore reduces potential interferences. > > The down side of this is that it needs DPDK support in guest, has this ever be > run on s390x guest? An alternative approach is to directly run XDP drop on > virtio-net nic in guest, while this requires compiling XDP inside guest which > needs > a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). > I made an attempt at DPDK, but it has not been run on s390x as far as I'm aware and didn't seem trivial to get working. So instead I took your alternate suggestion & did: pktgen(host) -> tap(x) -> guest(xdp_drop) When running this setup, I am not able to reproduce the regression. As mentioned previously, I am also unable to reproduce when running one end of the uperf connection from the host - I have only ever been able to reproduce when both ends of the uperf connection are running within a guest. > 3. BTW, did you enable hugepage for your guest? It would performance more > or less depends on the memory demand when generating traffic, I didn't see > similar command lines in yours. > s390x does not currently support passing through hugetlb backing via QEMU mem-path.
Re: Regression in throughput between kvm guests over virtual bridge
On Thu, Oct 05, 2017 at 04:07:45PM -0400, Matthew Rosato wrote: > > Ping... Jason, any other ideas or suggestions? Hi Matthew, Recently I am doing similar test on x86 for this patch, here are some, differences between our testbeds. 1. It is nice you have got improvement with 50+ instances(or connections here?) which would be quite helpful to address the issue, also you've figured out the cost(wait/wakeup), kindly reminder did you pin uperf client/server along the whole path besides vhost and vcpu threads? 2. It might be useful to short the traffic path as a reference, What I am running is briefly like: pktgen(host kernel) -> tap(x) -> guest(DPDK testpmd) The bridge driver(br_forward(), etc) might impact performance due to my personal experience, so eventually I settled down with this simplified testbed which fully isolates the traffic from both userspace and host kernel stack(1 and 50 instances, bridge driver, etc), therefore reduces potential interferences. The down side of this is that it needs DPDK support in guest, has this ever be run on s390x guest? An alternative approach is to directly run XDP drop on virtio-net nic in guest, while this requires compiling XDP inside guest which needs a newer distro(Fedora 25+ in my case or Ubuntu 16.10, not sure). 3. BTW, did you enable hugepage for your guest? It would performance more or less depends on the memory demand when generating traffic, I didn't see similar command lines in yours. Hope this doesn't make it more complicated for you.:) We will keep working on this and update you. Thanks, Wei >
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年10月06日 04:07, Matthew Rosato wrote: On 09/25/2017 04:18 PM, Matthew Rosato wrote: On 09/22/2017 12:03 AM, Jason Wang wrote: On 2017年09月21日 03:38, Matthew Rosato wrote: Seems to make some progress on wakeup mitigation. Previous patch tries to reduce the unnecessary traversal of waitqueue during rx. Attached patch goes even further which disables rx polling during processing tx. Please try it to see if it has any difference. Unfortunately, this patch doesn't seem to have made a difference. I tried runs with both this patch and the previous patch applied, as well as only this patch applied for comparison (numbers from vhost thread of sending VM): 4.12 4.13 patch1 patch2 patch1+2 2.00% +3.69% +2.55% +2.81% +2.69% [...] __wake_up_sync_key In each case, the regression in throughput was still present. This probably means some other cases of the wakeups were missed. Could you please record the callers of __wake_up_sync_key()? Hi Jason, With your 2 previous patches applied, every call to __wake_up_sync_key (for both sender and server vhost threads) shows the following stack trace: vhost-11478-11520 [002] 312.927229: __wake_up_sync_key <-sock_def_readable vhost-11478-11520 [002] 312.927230: => dev_hard_start_xmit => sch_direct_xmit => __dev_queue_xmit => br_dev_queue_push_xmit => br_forward_finish => __br_forward => br_handle_frame_finish => br_handle_frame => __netif_receive_skb_core => netif_receive_skb_internal => tun_get_user => tun_sendmsg => handle_tx => vhost_worker => kthread => kernel_thread_starter => kernel_thread_starter Ping... Jason, any other ideas or suggestions? Sorry for the late, recovering from a long holiday. Will go back to this soon. Thanks
Re: Regression in throughput between kvm guests over virtual bridge
On 09/25/2017 04:18 PM, Matthew Rosato wrote: > On 09/22/2017 12:03 AM, Jason Wang wrote: >> >> >> On 2017年09月21日 03:38, Matthew Rosato wrote: Seems to make some progress on wakeup mitigation. Previous patch tries to reduce the unnecessary traversal of waitqueue during rx. Attached patch goes even further which disables rx polling during processing tx. Please try it to see if it has any difference. >>> Unfortunately, this patch doesn't seem to have made a difference. I >>> tried runs with both this patch and the previous patch applied, as well >>> as only this patch applied for comparison (numbers from vhost thread of >>> sending VM): >>> >>> 4.12 4.13 patch1 patch2 patch1+2 >>> 2.00% +3.69% +2.55% +2.81% +2.69% [...] __wake_up_sync_key >>> >>> In each case, the regression in throughput was still present. >> >> This probably means some other cases of the wakeups were missed. Could >> you please record the callers of __wake_up_sync_key()? >> > > Hi Jason, > > With your 2 previous patches applied, every call to __wake_up_sync_key > (for both sender and server vhost threads) shows the following stack trace: > > vhost-11478-11520 [002] 312.927229: __wake_up_sync_key > <-sock_def_readable > vhost-11478-11520 [002] 312.927230: > => dev_hard_start_xmit > => sch_direct_xmit > => __dev_queue_xmit > => br_dev_queue_push_xmit > => br_forward_finish > => __br_forward > => br_handle_frame_finish > => br_handle_frame > => __netif_receive_skb_core > => netif_receive_skb_internal > => tun_get_user > => tun_sendmsg > => handle_tx > => vhost_worker > => kthread > => kernel_thread_starter > => kernel_thread_starter > Ping... Jason, any other ideas or suggestions?
Re: Regression in throughput between kvm guests over virtual bridge
On 09/22/2017 12:03 AM, Jason Wang wrote: > > > On 2017年09月21日 03:38, Matthew Rosato wrote: >>> Seems to make some progress on wakeup mitigation. Previous patch tries >>> to reduce the unnecessary traversal of waitqueue during rx. Attached >>> patch goes even further which disables rx polling during processing tx. >>> Please try it to see if it has any difference. >> Unfortunately, this patch doesn't seem to have made a difference. I >> tried runs with both this patch and the previous patch applied, as well >> as only this patch applied for comparison (numbers from vhost thread of >> sending VM): >> >> 4.12 4.13 patch1 patch2 patch1+2 >> 2.00% +3.69% +2.55% +2.81% +2.69% [...] __wake_up_sync_key >> >> In each case, the regression in throughput was still present. > > This probably means some other cases of the wakeups were missed. Could > you please record the callers of __wake_up_sync_key()? > Hi Jason, With your 2 previous patches applied, every call to __wake_up_sync_key (for both sender and server vhost threads) shows the following stack trace: vhost-11478-11520 [002] 312.927229: __wake_up_sync_key <-sock_def_readable vhost-11478-11520 [002] 312.927230: => dev_hard_start_xmit => sch_direct_xmit => __dev_queue_xmit => br_dev_queue_push_xmit => br_forward_finish => __br_forward => br_handle_frame_finish => br_handle_frame => __netif_receive_skb_core => netif_receive_skb_internal => tun_get_user => tun_sendmsg => handle_tx => vhost_worker => kthread => kernel_thread_starter => kernel_thread_starter >> >>> And two questions: >>> - Is the issue existed if you do uperf between 2VMs (instead of 4VMs) >> Verified that the second set of guests are not actually required, I can >> see the regression with only 2 VMs. >> >>> - Can enable batching in the tap of sending VM improve the performance >>> (ethtool -C $tap rx-frames 64) >> I tried this, but it did not help (actually seemed to make things a >> little worse) >> > > I still can't see a reason that can lead more wakeups, will take more > time to look at this issue and keep you posted. > > Thanks >
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月21日 03:38, Matthew Rosato wrote: Seems to make some progress on wakeup mitigation. Previous patch tries to reduce the unnecessary traversal of waitqueue during rx. Attached patch goes even further which disables rx polling during processing tx. Please try it to see if it has any difference. Unfortunately, this patch doesn't seem to have made a difference. I tried runs with both this patch and the previous patch applied, as well as only this patch applied for comparison (numbers from vhost thread of sending VM): 4.124.13 patch1 patch2 patch1+2 2.00% +3.69% +2.55% +2.81% +2.69% [...] __wake_up_sync_key In each case, the regression in throughput was still present. This probably means some other cases of the wakeups were missed. Could you please record the callers of __wake_up_sync_key()? And two questions: - Is the issue existed if you do uperf between 2VMs (instead of 4VMs) Verified that the second set of guests are not actually required, I can see the regression with only 2 VMs. - Can enable batching in the tap of sending VM improve the performance (ethtool -C $tap rx-frames 64) I tried this, but it did not help (actually seemed to make things a little worse) I still can't see a reason that can lead more wakeups, will take more time to look at this issue and keep you posted. Thanks
Re: Regression in throughput between kvm guests over virtual bridge
> Seems to make some progress on wakeup mitigation. Previous patch tries > to reduce the unnecessary traversal of waitqueue during rx. Attached > patch goes even further which disables rx polling during processing tx. > Please try it to see if it has any difference. Unfortunately, this patch doesn't seem to have made a difference. I tried runs with both this patch and the previous patch applied, as well as only this patch applied for comparison (numbers from vhost thread of sending VM): 4.124.13 patch1 patch2 patch1+2 2.00% +3.69% +2.55% +2.81% +2.69% [...] __wake_up_sync_key In each case, the regression in throughput was still present. > And two questions: > - Is the issue existed if you do uperf between 2VMs (instead of 4VMs) Verified that the second set of guests are not actually required, I can see the regression with only 2 VMs. > - Can enable batching in the tap of sending VM improve the performance > (ethtool -C $tap rx-frames 64) I tried this, but it did not help (actually seemed to make things a little worse)
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月19日 02:11, Matthew Rosato wrote: On 09/18/2017 03:36 AM, Jason Wang wrote: On 2017年09月18日 11:13, Jason Wang wrote: On 2017年09月16日 03:19, Matthew Rosato wrote: It looks like vhost is slowed down for some reason which leads to more idle time on 4.13+VHOST_RX_BATCH=1. Appreciated if you can collect the perf.diff on host, one for rx and one for tx. perf data below for the associated vhost threads, baseline=4.12, delta1=4.13, delta2=4.13+VHOST_RX_BATCH=1 Client vhost: 60.12% -11.11% -12.34% [kernel.vmlinux] [k] raw_copy_from_user 13.76% -1.28% -0.74% [kernel.vmlinux] [k] get_page_from_freelist 2.00% +3.69% +3.54% [kernel.vmlinux] [k] __wake_up_sync_key 1.19% +0.60% +0.66% [kernel.vmlinux] [k] __alloc_pages_nodemask 1.12% +0.76% +0.86% [kernel.vmlinux] [k] copy_page_from_iter 1.09% +0.28% +0.35% [vhost][k] vhost_get_vq_desc 1.07% +0.31% +0.26% [kernel.vmlinux] [k] alloc_skb_with_frags 0.94% +0.42% +0.65% [kernel.vmlinux] [k] alloc_pages_current 0.91% -0.19% -0.18% [kernel.vmlinux] [k] memcpy 0.88% +0.26% +0.30% [kernel.vmlinux] [k] __next_zones_zonelist 0.85% +0.05% +0.12% [kernel.vmlinux] [k] iov_iter_advance 0.79% +0.09% +0.19% [vhost][k] __vhost_add_used_n 0.74%[kernel.vmlinux] [k] get_task_policy.part.7 0.74% -0.01% -0.05% [kernel.vmlinux] [k] tun_net_xmit 0.60% +0.17% +0.33% [kernel.vmlinux] [k] policy_nodemask 0.58% -0.15% -0.12% [ebtables] [k] ebt_do_table 0.52% -0.25% -0.22% [kernel.vmlinux] [k] __alloc_skb ... 0.42% +0.58% +0.59% [kernel.vmlinux] [k] eventfd_signal ... 0.32% +0.96% +0.93% [kernel.vmlinux] [k] finish_task_switch ... +1.50% +1.16% [kernel.vmlinux] [k] get_task_policy.part.9 +0.40% +0.42% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.39% +0.40% [kernel.vmlinux] [k] _copy_from_iter_full +0.24% +0.23% [vhost_net][k] vhost_net_buf_peek Server vhost: 61.93% -10.72% -10.91% [kernel.vmlinux] [k] raw_copy_to_user 9.25% +0.47% +0.86% [kernel.vmlinux] [k] free_hot_cold_page 5.16% +1.41% +1.57% [vhost][k] vhost_get_vq_desc 5.12% -3.81% -3.78% [kernel.vmlinux] [k] skb_release_data 3.30% +0.42% +0.55% [kernel.vmlinux] [k] raw_copy_from_user 1.29% +2.20% +2.28% [kernel.vmlinux] [k] copy_page_to_iter 1.24% +1.65% +0.45% [vhost_net][k] handle_rx 1.08% +3.03% +2.85% [kernel.vmlinux] [k] __wake_up_sync_key 0.96% +0.70% +1.10% [vhost][k] translate_desc 0.69% -0.20% -0.22% [kernel.vmlinux] [k] tun_do_read.part.10 0.69%[kernel.vmlinux] [k] tun_peek_len 0.67% +0.75% +0.78% [kernel.vmlinux] [k] eventfd_signal 0.52% +0.96% +0.98% [kernel.vmlinux] [k] finish_task_switch 0.50% +0.05% +0.09% [vhost][k] vhost_add_used_n ... +0.63% +0.58% [vhost_net][k] vhost_net_buf_peek +0.32% +0.32% [kernel.vmlinux] [k] _copy_to_iter +0.19% +0.19% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.11% +0.21% [vhost][k] vhost_umem_interval_tr Looks like for some unknown reason which leads more wakeups. Could you please try to attached patch to see if it solves or mitigate the issue? Thanks My bad, please try this. Thanks Thanks Jason. Built 4.13 + supplied patch, I see some decrease in wakeups, but there's still quite a bit more compared to 4.12 (baseline=4.12, delta1=4.13, delta2=4.13+patch): client: 2.00% +3.69% +2.55% [kernel.vmlinux] [k] __wake_up_sync_key server: 1.08% +3.03% +1.85% [kernel.vmlinux] [k] __wake_up_sync_key Throughput was roughly equivalent to base 4.13 (so, still seeing the regression w/ this patch applied). Seems to make some progress on wakeup mitigation. Previous patch tries to reduce the unnecessary traversal of waitqueue during rx. Attached patch goes even further which disables rx polling during processing tx. Please try it to see if it has any difference. And two questions: - Is the issue existed if you do uperf between 2VMs (instead of 4VMs) - Can enable batching in the tap of sending VM improve the performance (ethtool -C $tap rx-frames 64) Thanks >From d57ad96083fc57205336af1b5ea777e5185f1581 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Wed, 20 Sep 2017 11:44:49 +0800 Subject: [PATCH] vhost_net: avoid unnecessary wakeups during tx Signed-off-by: Jason Wang --- drivers/vhost/net.c | 21 ++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index ed476fa..e7349cf 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -444,8 +444,11 @@ static bool vhost_exceeds_maxpend(struct vhost_net *n
Re: Regression in throughput between kvm guests over virtual bridge
On 09/18/2017 03:36 AM, Jason Wang wrote: > > > On 2017年09月18日 11:13, Jason Wang wrote: >> >> >> On 2017年09月16日 03:19, Matthew Rosato wrote: It looks like vhost is slowed down for some reason which leads to more idle time on 4.13+VHOST_RX_BATCH=1. Appreciated if you can collect the perf.diff on host, one for rx and one for tx. >>> perf data below for the associated vhost threads, baseline=4.12, >>> delta1=4.13, delta2=4.13+VHOST_RX_BATCH=1 >>> >>> Client vhost: >>> >>> 60.12% -11.11% -12.34% [kernel.vmlinux] [k] raw_copy_from_user >>> 13.76% -1.28% -0.74% [kernel.vmlinux] [k] get_page_from_freelist >>> 2.00% +3.69% +3.54% [kernel.vmlinux] [k] __wake_up_sync_key >>> 1.19% +0.60% +0.66% [kernel.vmlinux] [k] __alloc_pages_nodemask >>> 1.12% +0.76% +0.86% [kernel.vmlinux] [k] copy_page_from_iter >>> 1.09% +0.28% +0.35% [vhost][k] vhost_get_vq_desc >>> 1.07% +0.31% +0.26% [kernel.vmlinux] [k] alloc_skb_with_frags >>> 0.94% +0.42% +0.65% [kernel.vmlinux] [k] alloc_pages_current >>> 0.91% -0.19% -0.18% [kernel.vmlinux] [k] memcpy >>> 0.88% +0.26% +0.30% [kernel.vmlinux] [k] __next_zones_zonelist >>> 0.85% +0.05% +0.12% [kernel.vmlinux] [k] iov_iter_advance >>> 0.79% +0.09% +0.19% [vhost][k] __vhost_add_used_n >>> 0.74%[kernel.vmlinux] [k] get_task_policy.part.7 >>> 0.74% -0.01% -0.05% [kernel.vmlinux] [k] tun_net_xmit >>> 0.60% +0.17% +0.33% [kernel.vmlinux] [k] policy_nodemask >>> 0.58% -0.15% -0.12% [ebtables] [k] ebt_do_table >>> 0.52% -0.25% -0.22% [kernel.vmlinux] [k] __alloc_skb >>> ... >>> 0.42% +0.58% +0.59% [kernel.vmlinux] [k] eventfd_signal >>> ... >>> 0.32% +0.96% +0.93% [kernel.vmlinux] [k] finish_task_switch >>> ... >>> +1.50% +1.16% [kernel.vmlinux] [k] get_task_policy.part.9 >>> +0.40% +0.42% [kernel.vmlinux] [k] __skb_get_hash_symmetr >>> +0.39% +0.40% [kernel.vmlinux] [k] _copy_from_iter_full >>> +0.24% +0.23% [vhost_net][k] vhost_net_buf_peek >>> >>> Server vhost: >>> >>> 61.93% -10.72% -10.91% [kernel.vmlinux] [k] raw_copy_to_user >>> 9.25% +0.47% +0.86% [kernel.vmlinux] [k] free_hot_cold_page >>> 5.16% +1.41% +1.57% [vhost][k] vhost_get_vq_desc >>> 5.12% -3.81% -3.78% [kernel.vmlinux] [k] skb_release_data >>> 3.30% +0.42% +0.55% [kernel.vmlinux] [k] raw_copy_from_user >>> 1.29% +2.20% +2.28% [kernel.vmlinux] [k] copy_page_to_iter >>> 1.24% +1.65% +0.45% [vhost_net][k] handle_rx >>> 1.08% +3.03% +2.85% [kernel.vmlinux] [k] __wake_up_sync_key >>> 0.96% +0.70% +1.10% [vhost][k] translate_desc >>> 0.69% -0.20% -0.22% [kernel.vmlinux] [k] tun_do_read.part.10 >>> 0.69%[kernel.vmlinux] [k] tun_peek_len >>> 0.67% +0.75% +0.78% [kernel.vmlinux] [k] eventfd_signal >>> 0.52% +0.96% +0.98% [kernel.vmlinux] [k] finish_task_switch >>> 0.50% +0.05% +0.09% [vhost][k] vhost_add_used_n >>> ... >>> +0.63% +0.58% [vhost_net][k] vhost_net_buf_peek >>> +0.32% +0.32% [kernel.vmlinux] [k] _copy_to_iter >>> +0.19% +0.19% [kernel.vmlinux] [k] __skb_get_hash_symmetr >>> +0.11% +0.21% [vhost][k] vhost_umem_interval_tr >>> >> >> Looks like for some unknown reason which leads more wakeups. >> >> Could you please try to attached patch to see if it solves or mitigate >> the issue? >> >> Thanks > > My bad, please try this. > > Thanks Thanks Jason. Built 4.13 + supplied patch, I see some decrease in wakeups, but there's still quite a bit more compared to 4.12 (baseline=4.12, delta1=4.13, delta2=4.13+patch): client: 2.00% +3.69% +2.55% [kernel.vmlinux] [k] __wake_up_sync_key server: 1.08% +3.03% +1.85% [kernel.vmlinux] [k] __wake_up_sync_key Throughput was roughly equivalent to base 4.13 (so, still seeing the regression w/ this patch applied).
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月18日 11:13, Jason Wang wrote: On 2017年09月16日 03:19, Matthew Rosato wrote: It looks like vhost is slowed down for some reason which leads to more idle time on 4.13+VHOST_RX_BATCH=1. Appreciated if you can collect the perf.diff on host, one for rx and one for tx. perf data below for the associated vhost threads, baseline=4.12, delta1=4.13, delta2=4.13+VHOST_RX_BATCH=1 Client vhost: 60.12% -11.11% -12.34% [kernel.vmlinux] [k] raw_copy_from_user 13.76% -1.28% -0.74% [kernel.vmlinux] [k] get_page_from_freelist 2.00% +3.69% +3.54% [kernel.vmlinux] [k] __wake_up_sync_key 1.19% +0.60% +0.66% [kernel.vmlinux] [k] __alloc_pages_nodemask 1.12% +0.76% +0.86% [kernel.vmlinux] [k] copy_page_from_iter 1.09% +0.28% +0.35% [vhost] [k] vhost_get_vq_desc 1.07% +0.31% +0.26% [kernel.vmlinux] [k] alloc_skb_with_frags 0.94% +0.42% +0.65% [kernel.vmlinux] [k] alloc_pages_current 0.91% -0.19% -0.18% [kernel.vmlinux] [k] memcpy 0.88% +0.26% +0.30% [kernel.vmlinux] [k] __next_zones_zonelist 0.85% +0.05% +0.12% [kernel.vmlinux] [k] iov_iter_advance 0.79% +0.09% +0.19% [vhost] [k] __vhost_add_used_n 0.74% [kernel.vmlinux] [k] get_task_policy.part.7 0.74% -0.01% -0.05% [kernel.vmlinux] [k] tun_net_xmit 0.60% +0.17% +0.33% [kernel.vmlinux] [k] policy_nodemask 0.58% -0.15% -0.12% [ebtables] [k] ebt_do_table 0.52% -0.25% -0.22% [kernel.vmlinux] [k] __alloc_skb ... 0.42% +0.58% +0.59% [kernel.vmlinux] [k] eventfd_signal ... 0.32% +0.96% +0.93% [kernel.vmlinux] [k] finish_task_switch ... +1.50% +1.16% [kernel.vmlinux] [k] get_task_policy.part.9 +0.40% +0.42% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.39% +0.40% [kernel.vmlinux] [k] _copy_from_iter_full +0.24% +0.23% [vhost_net] [k] vhost_net_buf_peek Server vhost: 61.93% -10.72% -10.91% [kernel.vmlinux] [k] raw_copy_to_user 9.25% +0.47% +0.86% [kernel.vmlinux] [k] free_hot_cold_page 5.16% +1.41% +1.57% [vhost] [k] vhost_get_vq_desc 5.12% -3.81% -3.78% [kernel.vmlinux] [k] skb_release_data 3.30% +0.42% +0.55% [kernel.vmlinux] [k] raw_copy_from_user 1.29% +2.20% +2.28% [kernel.vmlinux] [k] copy_page_to_iter 1.24% +1.65% +0.45% [vhost_net] [k] handle_rx 1.08% +3.03% +2.85% [kernel.vmlinux] [k] __wake_up_sync_key 0.96% +0.70% +1.10% [vhost] [k] translate_desc 0.69% -0.20% -0.22% [kernel.vmlinux] [k] tun_do_read.part.10 0.69% [kernel.vmlinux] [k] tun_peek_len 0.67% +0.75% +0.78% [kernel.vmlinux] [k] eventfd_signal 0.52% +0.96% +0.98% [kernel.vmlinux] [k] finish_task_switch 0.50% +0.05% +0.09% [vhost] [k] vhost_add_used_n ... +0.63% +0.58% [vhost_net] [k] vhost_net_buf_peek +0.32% +0.32% [kernel.vmlinux] [k] _copy_to_iter +0.19% +0.19% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.11% +0.21% [vhost] [k] vhost_umem_interval_tr Looks like for some unknown reason which leads more wakeups. Could you please try to attached patch to see if it solves or mitigate the issue? Thanks My bad, please try this. Thanks >From 8be3edfcd415ba6157ab34d250127c6f2b21ff5d Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Mon, 18 Sep 2017 10:56:30 +0800 Subject: [PATCH] vhost_net: conditionally enable tx polling Signed-off-by: Jason Wang --- drivers/vhost/net.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 58585ec..2b308e0 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -471,6 +471,7 @@ static void handle_tx(struct vhost_net *net) goto out; vhost_disable_notify(&net->dev, vq); + vhost_net_disable_vq(net, vq); hdr_size = nvq->vhost_hlen; zcopy = nvq->ubufs; @@ -562,6 +563,8 @@ static void handle_tx(struct vhost_net *net) % UIO_MAXIOV; } vhost_discard_vq_desc(vq, 1); + if (err == -EAGAIN) +vhost_net_enable_vq(net, vq); break; } if (err != len) -- 2.7.4
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月16日 03:19, Matthew Rosato wrote: It looks like vhost is slowed down for some reason which leads to more idle time on 4.13+VHOST_RX_BATCH=1. Appreciated if you can collect the perf.diff on host, one for rx and one for tx. perf data below for the associated vhost threads, baseline=4.12, delta1=4.13, delta2=4.13+VHOST_RX_BATCH=1 Client vhost: 60.12% -11.11% -12.34% [kernel.vmlinux] [k] raw_copy_from_user 13.76% -1.28% -0.74% [kernel.vmlinux] [k] get_page_from_freelist 2.00% +3.69% +3.54% [kernel.vmlinux] [k] __wake_up_sync_key 1.19% +0.60% +0.66% [kernel.vmlinux] [k] __alloc_pages_nodemask 1.12% +0.76% +0.86% [kernel.vmlinux] [k] copy_page_from_iter 1.09% +0.28% +0.35% [vhost][k] vhost_get_vq_desc 1.07% +0.31% +0.26% [kernel.vmlinux] [k] alloc_skb_with_frags 0.94% +0.42% +0.65% [kernel.vmlinux] [k] alloc_pages_current 0.91% -0.19% -0.18% [kernel.vmlinux] [k] memcpy 0.88% +0.26% +0.30% [kernel.vmlinux] [k] __next_zones_zonelist 0.85% +0.05% +0.12% [kernel.vmlinux] [k] iov_iter_advance 0.79% +0.09% +0.19% [vhost][k] __vhost_add_used_n 0.74%[kernel.vmlinux] [k] get_task_policy.part.7 0.74% -0.01% -0.05% [kernel.vmlinux] [k] tun_net_xmit 0.60% +0.17% +0.33% [kernel.vmlinux] [k] policy_nodemask 0.58% -0.15% -0.12% [ebtables] [k] ebt_do_table 0.52% -0.25% -0.22% [kernel.vmlinux] [k] __alloc_skb ... 0.42% +0.58% +0.59% [kernel.vmlinux] [k] eventfd_signal ... 0.32% +0.96% +0.93% [kernel.vmlinux] [k] finish_task_switch ... +1.50% +1.16% [kernel.vmlinux] [k] get_task_policy.part.9 +0.40% +0.42% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.39% +0.40% [kernel.vmlinux] [k] _copy_from_iter_full +0.24% +0.23% [vhost_net][k] vhost_net_buf_peek Server vhost: 61.93% -10.72% -10.91% [kernel.vmlinux] [k] raw_copy_to_user 9.25% +0.47% +0.86% [kernel.vmlinux] [k] free_hot_cold_page 5.16% +1.41% +1.57% [vhost][k] vhost_get_vq_desc 5.12% -3.81% -3.78% [kernel.vmlinux] [k] skb_release_data 3.30% +0.42% +0.55% [kernel.vmlinux] [k] raw_copy_from_user 1.29% +2.20% +2.28% [kernel.vmlinux] [k] copy_page_to_iter 1.24% +1.65% +0.45% [vhost_net][k] handle_rx 1.08% +3.03% +2.85% [kernel.vmlinux] [k] __wake_up_sync_key 0.96% +0.70% +1.10% [vhost][k] translate_desc 0.69% -0.20% -0.22% [kernel.vmlinux] [k] tun_do_read.part.10 0.69%[kernel.vmlinux] [k] tun_peek_len 0.67% +0.75% +0.78% [kernel.vmlinux] [k] eventfd_signal 0.52% +0.96% +0.98% [kernel.vmlinux] [k] finish_task_switch 0.50% +0.05% +0.09% [vhost][k] vhost_add_used_n ... +0.63% +0.58% [vhost_net][k] vhost_net_buf_peek +0.32% +0.32% [kernel.vmlinux] [k] _copy_to_iter +0.19% +0.19% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.11% +0.21% [vhost][k] vhost_umem_interval_tr Looks like for some unknown reason which leads more wakeups. Could you please try to attached patch to see if it solves or mitigate the issue? Thanks >From 63b276ed881c1e2a89b7ea35b6f328f70ddd6185 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Mon, 18 Sep 2017 10:56:30 +0800 Subject: [PATCH] vhost_net: conditionally enable tx polling Signed-off-by: Jason Wang --- drivers/vhost/net.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 58585ec..397d86a 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -471,6 +471,7 @@ static void handle_tx(struct vhost_net *net) goto out; vhost_disable_notify(&net->dev, vq); + vhost_net_disable_vq(net, vq); hdr_size = nvq->vhost_hlen; zcopy = nvq->ubufs; @@ -562,6 +563,8 @@ static void handle_tx(struct vhost_net *net) % UIO_MAXIOV; } vhost_discard_vq_desc(vq, 1); + if (err = -EAGAIN) +vhost_net_enable_vq(net, vq); break; } if (err != len) -- 1.8.3.1
Re: Regression in throughput between kvm guests over virtual bridge
> It looks like vhost is slowed down for some reason which leads to more > idle time on 4.13+VHOST_RX_BATCH=1. Appreciated if you can collect the > perf.diff on host, one for rx and one for tx. > perf data below for the associated vhost threads, baseline=4.12, delta1=4.13, delta2=4.13+VHOST_RX_BATCH=1 Client vhost: 60.12% -11.11% -12.34% [kernel.vmlinux] [k] raw_copy_from_user 13.76% -1.28% -0.74% [kernel.vmlinux] [k] get_page_from_freelist 2.00% +3.69% +3.54% [kernel.vmlinux] [k] __wake_up_sync_key 1.19% +0.60% +0.66% [kernel.vmlinux] [k] __alloc_pages_nodemask 1.12% +0.76% +0.86% [kernel.vmlinux] [k] copy_page_from_iter 1.09% +0.28% +0.35% [vhost][k] vhost_get_vq_desc 1.07% +0.31% +0.26% [kernel.vmlinux] [k] alloc_skb_with_frags 0.94% +0.42% +0.65% [kernel.vmlinux] [k] alloc_pages_current 0.91% -0.19% -0.18% [kernel.vmlinux] [k] memcpy 0.88% +0.26% +0.30% [kernel.vmlinux] [k] __next_zones_zonelist 0.85% +0.05% +0.12% [kernel.vmlinux] [k] iov_iter_advance 0.79% +0.09% +0.19% [vhost][k] __vhost_add_used_n 0.74%[kernel.vmlinux] [k] get_task_policy.part.7 0.74% -0.01% -0.05% [kernel.vmlinux] [k] tun_net_xmit 0.60% +0.17% +0.33% [kernel.vmlinux] [k] policy_nodemask 0.58% -0.15% -0.12% [ebtables] [k] ebt_do_table 0.52% -0.25% -0.22% [kernel.vmlinux] [k] __alloc_skb ... 0.42% +0.58% +0.59% [kernel.vmlinux] [k] eventfd_signal ... 0.32% +0.96% +0.93% [kernel.vmlinux] [k] finish_task_switch ... +1.50% +1.16% [kernel.vmlinux] [k] get_task_policy.part.9 +0.40% +0.42% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.39% +0.40% [kernel.vmlinux] [k] _copy_from_iter_full +0.24% +0.23% [vhost_net][k] vhost_net_buf_peek Server vhost: 61.93% -10.72% -10.91% [kernel.vmlinux] [k] raw_copy_to_user 9.25% +0.47% +0.86% [kernel.vmlinux] [k] free_hot_cold_page 5.16% +1.41% +1.57% [vhost][k] vhost_get_vq_desc 5.12% -3.81% -3.78% [kernel.vmlinux] [k] skb_release_data 3.30% +0.42% +0.55% [kernel.vmlinux] [k] raw_copy_from_user 1.29% +2.20% +2.28% [kernel.vmlinux] [k] copy_page_to_iter 1.24% +1.65% +0.45% [vhost_net][k] handle_rx 1.08% +3.03% +2.85% [kernel.vmlinux] [k] __wake_up_sync_key 0.96% +0.70% +1.10% [vhost][k] translate_desc 0.69% -0.20% -0.22% [kernel.vmlinux] [k] tun_do_read.part.10 0.69%[kernel.vmlinux] [k] tun_peek_len 0.67% +0.75% +0.78% [kernel.vmlinux] [k] eventfd_signal 0.52% +0.96% +0.98% [kernel.vmlinux] [k] finish_task_switch 0.50% +0.05% +0.09% [vhost][k] vhost_add_used_n ... +0.63% +0.58% [vhost_net][k] vhost_net_buf_peek +0.32% +0.32% [kernel.vmlinux] [k] _copy_to_iter +0.19% +0.19% [kernel.vmlinux] [k] __skb_get_hash_symmetr +0.11% +0.21% [vhost][k] vhost_umem_interval_tr
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月15日 11:36, Matthew Rosato wrote: Is the issue gone if you reduce VHOST_RX_BATCH to 1? And it would be also helpful to collect perf diff to see if anything interesting. (Consider 4.4 shows more obvious regression, please use 4.4). Issue still exists when I force VHOST_RX_BATCH = 1 Interesting, so this looks more like an issue of the changes in vhost_net instead of batch dequeuing itself. I try this on Intel but still can't meet it. Collected perf data, with 4.12 as the baseline, 4.13 as delta1 and 4.13+VHOST_RX_BATCH=1 as delta2. All guests running 4.4. Same scenario, 2 uperf client guests, 2 uperf slave guests - I collected perf data against 1 uperf client process and 1 uperf slave process. Here are the significant diffs: uperf client: 75.09% +9.32% +8.52% [kernel.kallsyms] [k] enabled_wait 9.04% -4.11% -3.79% [kernel.kallsyms] [k] __copy_from_user 2.30% -0.79% -0.71% [kernel.kallsyms] [k] arch_free_page 2.17% -0.65% -0.58% [kernel.kallsyms] [k] arch_alloc_page 0.69% -0.25% -0.24% [kernel.kallsyms] [k] get_page_from_freelist 0.56% +0.08% +0.14% [kernel.kallsyms] [k] virtio_ccw_kvm_notify 0.42% -0.11% -0.09% [kernel.kallsyms] [k] tcp_sendmsg 0.31% -0.15% -0.14% [kernel.kallsyms] [k] tcp_write_xmit uperf slave: 72.44% +8.99% +8.85% [kernel.kallsyms] [k] enabled_wait 8.99% -3.67% -3.51% [kernel.kallsyms] [k] __copy_to_user 2.31% -0.71% -0.67% [kernel.kallsyms] [k] arch_free_page 2.16% -0.67% -0.63% [kernel.kallsyms] [k] arch_alloc_page 0.89% -0.14% -0.11% [kernel.kallsyms] [k] virtio_ccw_kvm_notify 0.71% -0.30% -0.30% [kernel.kallsyms] [k] get_page_from_freelist 0.70% -0.25% -0.29% [kernel.kallsyms] [k] __wake_up_sync_key 0.61% -0.22% -0.22% [kernel.kallsyms] [k] virtqueue_add_inbuf It looks like vhost is slowed down for some reason which leads to more idle time on 4.13+VHOST_RX_BATCH=1. Appreciated if you can collect the perf.diff on host, one for rx and one for tx. May worth to try disable zerocopy or do the test form host to guest instead of guest to guest to exclude the possible issue of sender. With zerocopy disabled, still seeing the regression. The provided perf #s have zerocopy enabled. I replaced 1 uperf guest and instead ran that uperf client as a host process, pointing at a guest. All traffic still over the virtual bridge. In this setup, it's still easy to see the regression for the remaining guest1<->guest2 uperf run, but the host<->guest3 run does NOT exhibit a reliable regression pattern. The significant perf diffs from the host uperf process (baseline=4.12, delta=4.13): 59.96% +5.03% [kernel.kallsyms] [k] enabled_wait 6.47% -2.27% [kernel.kallsyms] [k] raw_copy_to_user 5.52% -1.63% [kernel.kallsyms] [k] raw_copy_from_user 0.87% -0.30% [kernel.kallsyms] [k] get_page_from_freelist 0.69% +0.30% [kernel.kallsyms] [k] finish_task_switch 0.66% -0.15% [kernel.kallsyms] [k] swake_up 0.58% -0.00% [vhost] [k] vhost_get_vq_desc ... 0.42% +0.50% [kernel.kallsyms] [k] ckc_irq_pending Another hint to perf vhost threads. I also tried flipping the uperf stream around (a guest uperf client is communicating to a slave uperf process on the host) and also cannot see the regression pattern. So it seems to require a guest on both ends of the connection. Yes. Will try to get a s390 environment. Thanks
Re: Regression in throughput between kvm guests over virtual bridge
> Is the issue gone if you reduce VHOST_RX_BATCH to 1? And it would be > also helpful to collect perf diff to see if anything interesting. > (Consider 4.4 shows more obvious regression, please use 4.4). > Issue still exists when I force VHOST_RX_BATCH = 1 Collected perf data, with 4.12 as the baseline, 4.13 as delta1 and 4.13+VHOST_RX_BATCH=1 as delta2. All guests running 4.4. Same scenario, 2 uperf client guests, 2 uperf slave guests - I collected perf data against 1 uperf client process and 1 uperf slave process. Here are the significant diffs: uperf client: 75.09% +9.32% +8.52% [kernel.kallsyms] [k] enabled_wait 9.04% -4.11% -3.79% [kernel.kallsyms] [k] __copy_from_user 2.30% -0.79% -0.71% [kernel.kallsyms] [k] arch_free_page 2.17% -0.65% -0.58% [kernel.kallsyms] [k] arch_alloc_page 0.69% -0.25% -0.24% [kernel.kallsyms] [k] get_page_from_freelist 0.56% +0.08% +0.14% [kernel.kallsyms] [k] virtio_ccw_kvm_notify 0.42% -0.11% -0.09% [kernel.kallsyms] [k] tcp_sendmsg 0.31% -0.15% -0.14% [kernel.kallsyms] [k] tcp_write_xmit uperf slave: 72.44% +8.99% +8.85% [kernel.kallsyms] [k] enabled_wait 8.99% -3.67% -3.51% [kernel.kallsyms] [k] __copy_to_user 2.31% -0.71% -0.67% [kernel.kallsyms] [k] arch_free_page 2.16% -0.67% -0.63% [kernel.kallsyms] [k] arch_alloc_page 0.89% -0.14% -0.11% [kernel.kallsyms] [k] virtio_ccw_kvm_notify 0.71% -0.30% -0.30% [kernel.kallsyms] [k] get_page_from_freelist 0.70% -0.25% -0.29% [kernel.kallsyms] [k] __wake_up_sync_key 0.61% -0.22% -0.22% [kernel.kallsyms] [k] virtqueue_add_inbuf > > May worth to try disable zerocopy or do the test form host to guest > instead of guest to guest to exclude the possible issue of sender. > With zerocopy disabled, still seeing the regression. The provided perf #s have zerocopy enabled. I replaced 1 uperf guest and instead ran that uperf client as a host process, pointing at a guest. All traffic still over the virtual bridge. In this setup, it's still easy to see the regression for the remaining guest1<->guest2 uperf run, but the host<->guest3 run does NOT exhibit a reliable regression pattern. The significant perf diffs from the host uperf process (baseline=4.12, delta=4.13): 59.96% +5.03% [kernel.kallsyms] [k] enabled_wait 6.47% -2.27% [kernel.kallsyms] [k] raw_copy_to_user 5.52% -1.63% [kernel.kallsyms] [k] raw_copy_from_user 0.87% -0.30% [kernel.kallsyms] [k] get_page_from_freelist 0.69% +0.30% [kernel.kallsyms] [k] finish_task_switch 0.66% -0.15% [kernel.kallsyms] [k] swake_up 0.58% -0.00% [vhost] [k] vhost_get_vq_desc ... 0.42% +0.50% [kernel.kallsyms] [k] ckc_irq_pending I also tried flipping the uperf stream around (a guest uperf client is communicating to a slave uperf process on the host) and also cannot see the regression pattern. So it seems to require a guest on both ends of the connection.
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月14日 00:59, Matthew Rosato wrote: On 09/13/2017 04:13 AM, Jason Wang wrote: On 2017年09月13日 09:16, Jason Wang wrote: On 2017年09月13日 01:56, Matthew Rosato wrote: We are seeing a regression for a subset of workloads across KVM guests over a virtual bridge between host kernel 4.12 and 4.13. Bisecting points to c67df11f "vhost_net: try batch dequing from skb array" In the regressed environment, we are running 4 kvm guests, 2 running as uperf servers and 2 running as uperf clients, all on a single host. They are connected via a virtual bridge. The uperf client profile looks like: So, 1 tcp streaming instance per client. When upgrading the host kernel from 4.12->4.13, we see about a 30% drop in throughput for this scenario. After the bisect, I further verified that reverting c67df11f on 4.13 "fixes" the throughput for this scenario. On the other hand, if we increase the load by upping the number of streaming instances to 50 (nprocs="50") or even 10, we see instead a ~10% increase in throughput when upgrading host from 4.12->4.13. So it may be the issue is specific to "light load" scenarios. I would expect some overhead for the batching, but 30% seems significant... Any thoughts on what might be happening here? Hi, thanks for the bisecting. Will try to see if I can reproduce. Various factors could have impact on stream performance. If possible, could you collect the #pkts and average packet size during the test? And if you guest version is above 4.12, could you please retry with napi_tx=true? Original runs were done with guest kernel 4.4 (from ubuntu 16.04.3 - 4.4.0-93-generic specifically). Here's a throughput report (uperf) and #pkts and average packet size (tcpstat) for one of the uperf clients: host 4.12 / guest 4.4: throughput: 29.98Gb/s #pkts=33465571 avg packet size=33755.70 host 4.13 / guest 4.4: throughput: 20.36Gb/s #pkts=21233399 avg packet size=36130.69 I test guest 4.4 on Intel machine, still can reproduce :( I ran the test again using net-next.git as guest kernel, with and without napi_tx=true. napi_tx did not seem to have any significant impact on throughput. However, the guest kernel shift from 4.4->net-next improved things. I can still see a regression between host 4.12 and 4.13, but it's more on the order of 10-15% - another sample: host 4.12 / guest net-next (without napi_tx): throughput: 28.88Gb/s #pkts=31743116 avg packet size=33779.78 host 4.13 / guest net-next (without napi_tx): throughput: 24.34Gb/s #pkts=25532724 avg packet size=35963.20 Thanks for the numbers. I originally suspect batching will lead more pkts but less size, but looks not. The less packets is also a hint that there's delay somewhere. Thanks Unfortunately, I could not reproduce it locally. I'm using net-next.git as guest. I can get ~42Gb/s on Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz for both before and after the commit. I use 1 vcpu and 1 queue, and pin vcpu and vhost threads into separate cpu on host manually (in same numa node). The environment is quite a bit different -- I'm running in an LPAR on a z13 (s390x). We've seen the issue in various configurations, the smallest thus far was a host partition w/ 40G and 20 CPUs defined (the numbers above were gathered w/ this configuration). Each guest has 4GB and 4 vcpus. No pinning / affinity configured. Unfortunately, I don't have s390x on hand. Will try to get one. Can you hit this regression constantly and what's you qemu command line Yes, the regression seems consistent. I can try tweaking some of the host and guest definitions to see if it makes a difference. Is the issue gone if you reduce VHOST_RX_BATCH to 1? And it would be also helpful to collect perf diff to see if anything interesting. (Consider 4.4 shows more obvious regression, please use 4.4). The guests are instantiated from libvirt - Here's one of the resulting qemu command lines: /usr/bin/qemu-system-s390x -name guest=mjrs34g1,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-mjrs34g1/master-key.aes -machine s390-ccw-virtio-2.10,accel=kvm,usb=off,dump-guest-core=off -m 4096 -realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid 44710587-e783-4bd8-8590-55ff421431b1 -display none -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-1-mjrs34g1/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -drive file=/dev/disk/by-id/scsi-3600507630bffc0381803,format=raw,if=none,id=drive-virtio-disk0 -device virtio-blk-ccw,scsi=off,devno=fe.0.,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=27 -device virtio-net-ccw,netdev=hostnet0,id=net0,mac=02:de:26:53:14:01,devno=fe.0.0001 -netdev tap,fd=28,id=hostnet1,vhost=on,vhostfd=29 -device virtio-net-ccw
Re: Regression in throughput between kvm guests over virtual bridge
On 09/13/2017 04:13 AM, Jason Wang wrote: > > > On 2017年09月13日 09:16, Jason Wang wrote: >> >> >> On 2017年09月13日 01:56, Matthew Rosato wrote: >>> We are seeing a regression for a subset of workloads across KVM guests >>> over a virtual bridge between host kernel 4.12 and 4.13. Bisecting >>> points to c67df11f "vhost_net: try batch dequing from skb array" >>> >>> In the regressed environment, we are running 4 kvm guests, 2 running as >>> uperf servers and 2 running as uperf clients, all on a single host. >>> They are connected via a virtual bridge. The uperf client profile looks >>> like: >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> So, 1 tcp streaming instance per client. When upgrading the host kernel >>> from 4.12->4.13, we see about a 30% drop in throughput for this >>> scenario. After the bisect, I further verified that reverting c67df11f >>> on 4.13 "fixes" the throughput for this scenario. >>> >>> On the other hand, if we increase the load by upping the number of >>> streaming instances to 50 (nprocs="50") or even 10, we see instead a >>> ~10% increase in throughput when upgrading host from 4.12->4.13. >>> >>> So it may be the issue is specific to "light load" scenarios. I would >>> expect some overhead for the batching, but 30% seems significant... Any >>> thoughts on what might be happening here? >>> >> >> Hi, thanks for the bisecting. Will try to see if I can reproduce. >> Various factors could have impact on stream performance. If possible, >> could you collect the #pkts and average packet size during the test? >> And if you guest version is above 4.12, could you please retry with >> napi_tx=true? Original runs were done with guest kernel 4.4 (from ubuntu 16.04.3 - 4.4.0-93-generic specifically). Here's a throughput report (uperf) and #pkts and average packet size (tcpstat) for one of the uperf clients: host 4.12 / guest 4.4: throughput: 29.98Gb/s #pkts=33465571 avg packet size=33755.70 host 4.13 / guest 4.4: throughput: 20.36Gb/s #pkts=21233399 avg packet size=36130.69 I ran the test again using net-next.git as guest kernel, with and without napi_tx=true. napi_tx did not seem to have any significant impact on throughput. However, the guest kernel shift from 4.4->net-next improved things. I can still see a regression between host 4.12 and 4.13, but it's more on the order of 10-15% - another sample: host 4.12 / guest net-next (without napi_tx): throughput: 28.88Gb/s #pkts=31743116 avg packet size=33779.78 host 4.13 / guest net-next (without napi_tx): throughput: 24.34Gb/s #pkts=25532724 avg packet size=35963.20 >> >> Thanks > > Unfortunately, I could not reproduce it locally. I'm using net-next.git > as guest. I can get ~42Gb/s on Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz > for both before and after the commit. I use 1 vcpu and 1 queue, and pin > vcpu and vhost threads into separate cpu on host manually (in same numa > node). The environment is quite a bit different -- I'm running in an LPAR on a z13 (s390x). We've seen the issue in various configurations, the smallest thus far was a host partition w/ 40G and 20 CPUs defined (the numbers above were gathered w/ this configuration). Each guest has 4GB and 4 vcpus. No pinning / affinity configured. > > Can you hit this regression constantly and what's you qemu command line Yes, the regression seems consistent. I can try tweaking some of the host and guest definitions to see if it makes a difference. The guests are instantiated from libvirt - Here's one of the resulting qemu command lines: /usr/bin/qemu-system-s390x -name guest=mjrs34g1,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-mjrs34g1/master-key.aes -machine s390-ccw-virtio-2.10,accel=kvm,usb=off,dump-guest-core=off -m 4096 -realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid 44710587-e783-4bd8-8590-55ff421431b1 -display none -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-1-mjrs34g1/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -drive file=/dev/disk/by-id/scsi-3600507630bffc0381803,format=raw,if=none,id=drive-virtio-disk0 -device virtio-blk-ccw,scsi=off,devno=fe.0.,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=27 -device virtio-net-ccw,netdev=hostnet0,id=net0,mac=02:de:26:53:14:01,devno=fe.0.0001 -netdev tap,fd=28,id=hostnet1,vhost=on,vhostfd=29 -device virtio-net-ccw,netdev=hostnet1,id=net1,mac=02:54:00:89:d4:01,devno=fe.0.00a1 -chardev pty,id=charconsole0 -device sclpconsole,chardev=charconsole0,id=console0 -device virtio-balloon-ccw,id=balloon0,devno=fe.0.0002 -msg timestamp=on In the above, net0 is used for a macvtap connection (not used in the experiment, just for a reliable ssh connection - can remove if needed). net1 is the br
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月13日 09:16, Jason Wang wrote: On 2017年09月13日 01:56, Matthew Rosato wrote: We are seeing a regression for a subset of workloads across KVM guests over a virtual bridge between host kernel 4.12 and 4.13. Bisecting points to c67df11f "vhost_net: try batch dequing from skb array" In the regressed environment, we are running 4 kvm guests, 2 running as uperf servers and 2 running as uperf clients, all on a single host. They are connected via a virtual bridge. The uperf client profile looks like: So, 1 tcp streaming instance per client. When upgrading the host kernel from 4.12->4.13, we see about a 30% drop in throughput for this scenario. After the bisect, I further verified that reverting c67df11f on 4.13 "fixes" the throughput for this scenario. On the other hand, if we increase the load by upping the number of streaming instances to 50 (nprocs="50") or even 10, we see instead a ~10% increase in throughput when upgrading host from 4.12->4.13. So it may be the issue is specific to "light load" scenarios. I would expect some overhead for the batching, but 30% seems significant... Any thoughts on what might be happening here? Hi, thanks for the bisecting. Will try to see if I can reproduce. Various factors could have impact on stream performance. If possible, could you collect the #pkts and average packet size during the test? And if you guest version is above 4.12, could you please retry with napi_tx=true? Thanks Unfortunately, I could not reproduce it locally. I'm using net-next.git as guest. I can get ~42Gb/s on Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz for both before and after the commit. I use 1 vcpu and 1 queue, and pin vcpu and vhost threads into separate cpu on host manually (in same numa node). Can you hit this regression constantly and what's you qemu command line and #cpus on host? Is zerocopy enabled? Thanks
Re: Regression in throughput between kvm guests over virtual bridge
On 2017年09月13日 01:56, Matthew Rosato wrote: We are seeing a regression for a subset of workloads across KVM guests over a virtual bridge between host kernel 4.12 and 4.13. Bisecting points to c67df11f "vhost_net: try batch dequing from skb array" In the regressed environment, we are running 4 kvm guests, 2 running as uperf servers and 2 running as uperf clients, all on a single host. They are connected via a virtual bridge. The uperf client profile looks like: So, 1 tcp streaming instance per client. When upgrading the host kernel from 4.12->4.13, we see about a 30% drop in throughput for this scenario. After the bisect, I further verified that reverting c67df11f on 4.13 "fixes" the throughput for this scenario. On the other hand, if we increase the load by upping the number of streaming instances to 50 (nprocs="50") or even 10, we see instead a ~10% increase in throughput when upgrading host from 4.12->4.13. So it may be the issue is specific to "light load" scenarios. I would expect some overhead for the batching, but 30% seems significant... Any thoughts on what might be happening here? Hi, thanks for the bisecting. Will try to see if I can reproduce. Various factors could have impact on stream performance. If possible, could you collect the #pkts and average packet size during the test? And if you guest version is above 4.12, could you please retry with napi_tx=true? Thanks
Regression in throughput between kvm guests over virtual bridge
We are seeing a regression for a subset of workloads across KVM guests over a virtual bridge between host kernel 4.12 and 4.13. Bisecting points to c67df11f "vhost_net: try batch dequing from skb array" In the regressed environment, we are running 4 kvm guests, 2 running as uperf servers and 2 running as uperf clients, all on a single host. They are connected via a virtual bridge. The uperf client profile looks like: So, 1 tcp streaming instance per client. When upgrading the host kernel from 4.12->4.13, we see about a 30% drop in throughput for this scenario. After the bisect, I further verified that reverting c67df11f on 4.13 "fixes" the throughput for this scenario. On the other hand, if we increase the load by upping the number of streaming instances to 50 (nprocs="50") or even 10, we see instead a ~10% increase in throughput when upgrading host from 4.12->4.13. So it may be the issue is specific to "light load" scenarios. I would expect some overhead for the batching, but 30% seems significant... Any thoughts on what might be happening here?
