On Wed, Jul 19, 2023 at 03:53:45PM +0800, Hawkins Jiawei wrote: > This patchset allows QEMU to delay polling and checking the device > used buffer until either the SVQ is full or control commands shadow > buffers are full, instead of polling and checking immediately after > sending each SVQ control command, so that QEMU can send all the SVQ > control commands in parallel, which have better performance improvement. > > I use vp_vdpa device to simulate vdpa device, and create 4094 VLANS in > guest to build a test environment for sending multiple CVQ state load > commands. This patch series can improve latency from 10023 us to > 8697 us for about 4099 CVQ state load commands, about 0.32 us per command.
Looks like a tiny improvement. At the same time we have O(n^2) behaviour with memory mappings. Not saying we must not do this but I think it's worth checking where the bottleneck is. My guess would be vp_vdpa is not doing things in parallel. Want to try fixing that to see how far it can be pushed? > Note that this patch should be based on > patch "Vhost-vdpa Shadow Virtqueue VLAN support" at [1]. > > [1]. https://lists.gnu.org/archive/html/qemu-devel/2023-07/msg03719.html > > TestStep > ======== > 1. regression testing using vp-vdpa device > - For L0 guest, boot QEMU with two virtio-net-pci net device with > `ctrl_vq`, `ctrl_rx`, `ctrl_rx_extra` features on, command line like: > -device virtio-net-pci,disable-legacy=on,disable-modern=off, > iommu_platform=on,mq=on,ctrl_vq=on,guest_announce=off, > indirect_desc=off,queue_reset=off,ctrl_rx=on,ctrl_rx_extra=on,... > > - For L1 guest, apply the patch series and compile the source code, > start QEMU with two vdpa device with svq mode on, enable the `ctrl_vq`, > `ctrl_rx`, `ctrl_rx_extra` features on, command line like: > -netdev type=vhost-vdpa,x-svq=true,... > -device virtio-net-pci,mq=on,guest_announce=off,ctrl_vq=on, > ctrl_rx=on,ctrl_rx_extra=on... > > - For L2 source guest, run the following bash command: > ```bash > #!/bin/sh > > for idx1 in {0..9} > do > for idx2 in {0..9} > do > for idx3 in {0..6} > do > ip link add macvlan$idx1$idx2$idx3 link eth0 > address 4a:30:10:19:$idx1$idx2:1$idx3 type macvlan mode bridge > ip link set macvlan$idx1$idx2$idx3 up > done > done > done > ``` > - Execute the live migration in L2 source monitor > > - Result > * with this series, QEMU should not trigger any error or warning. > > > > 2. perf using vp-vdpa device > - For L0 guest, boot QEMU with two virtio-net-pci net device with > `ctrl_vq`, `ctrl_vlan` features on, command line like: > -device virtio-net-pci,disable-legacy=on,disable-modern=off, > iommu_platform=on,mq=on,ctrl_vq=on,guest_announce=off, > indirect_desc=off,queue_reset=off,ctrl_vlan=on,... > > - For L1 guest, apply the patch series, then apply an addtional > patch to record the load time in microseconds as following: > ```diff > diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c > index 6b958d6363..501b510fd2 100644 > --- a/hw/net/vhost_net.c > +++ b/hw/net/vhost_net.c > @@ -295,7 +295,10 @@ static int vhost_net_start_one(struct vhost_net *net, > } > > if (net->nc->info->load) { > + int64_t start_us = g_get_monotonic_time(); > r = net->nc->info->load(net->nc); > + error_report("vhost_vdpa_net_load() = %ld us", > + g_get_monotonic_time() - start_us); > if (r < 0) { > goto fail; > } > ``` > > - For L1 guest, compile the code, and start QEMU with two vdpa device > with svq mode on, enable the `ctrl_vq`, `ctrl_vlan` features on, > command line like: > -netdev type=vhost-vdpa,x-svq=true,... > -device virtio-net-pci,mq=on,guest_announce=off,ctrl_vq=on, > ctrl_vlan=on... > > - For L2 source guest, run the following bash command: > ```bash > #!/bin/sh > > for idx in {1..4094} > do > ip link add link eth0 name vlan$idx type vlan id $idx > done > ``` > > - wait for some time, then execute the live migration in L2 source monitor > > - Result > * with this series, QEMU should not trigger any warning > or error except something like "vhost_vdpa_net_load() = 8697 us" > * without this series, QEMU should not trigger any warning > or error except something like "vhost_vdpa_net_load() = 10023 us" > > ChangeLog > ========= > v3: > - refactor vhost_svq_poll() to accept cmds_in_flight > suggested by Jason and Eugenio > - refactor vhost_vdpa_net_cvq_add() to make control commands buffers > is not tied to `s->cvq_cmd_out_buffer` and `s->status`, so we can reuse > it suggested by Eugenio > - poll and check when SVQ is full or control commands shadow buffers is > full > > v2: https://lore.kernel.org/all/cover.1683371965.git.yin31...@gmail.com/ > - recover accidentally deleted rows > - remove extra newline > - refactor `need_poll_len` to `cmds_in_flight` > - return -EINVAL when vhost_svq_poll() return 0 or check > on buffers written by device fails > - change the type of `in_cursor`, and refactor the > code for updating cursor > - return directly when vhost_vdpa_net_load_{mac,mq}() > returns a failure in vhost_vdpa_net_load() > > v1: https://lore.kernel.org/all/cover.1681732982.git.yin31...@gmail.com/ > > Hawkins Jiawei (8): > vhost: Add argument to vhost_svq_poll() > vdpa: Use iovec for vhost_vdpa_net_cvq_add() > vhost: Expose vhost_svq_available_slots() > vdpa: Avoid using vhost_vdpa_net_load_*() outside > vhost_vdpa_net_load() > vdpa: Check device ack in vhost_vdpa_net_load_rx_mode() > vdpa: Move vhost_svq_poll() to the caller of vhost_vdpa_net_cvq_add() > vdpa: Add cursors to vhost_vdpa_net_loadx() > vdpa: Send cvq state load commands in parallel > > hw/virtio/vhost-shadow-virtqueue.c | 38 ++-- > hw/virtio/vhost-shadow-virtqueue.h | 3 +- > net/vhost-vdpa.c | 354 ++++++++++++++++++----------- > 3 files changed, 249 insertions(+), 146 deletions(-) > > -- > 2.25.1
