Right, you might want to review Documentation/timers/no_hz.rst from the kernel sources and look for RCU implications section where it explains how to move RCU callbacks.
fbl On Tue, Jun 30, 2020 at 12:08:05PM -0400, Shahaji Bhosle wrote: > Hi Flavio, > I wrote a small program which has do_nothing for loop and I measure the > timestamps across the do nothing loop. I am seeing 3% of the time around > the 1 second mark when the arch_timer fires I get the timestamps to be off > by 25% of the exprected value. I ran trace-cmd to see what is going on and > see the below. Looks like some issue with *gic_handle_irg*(), not seeing > tihs behaviour on x86 host, something special with ARM v8. > Thanks, Shahaji > > %21.77 (14181) arm_stb_user_lo rcu_dyntick #922 > | > --- *rcu_dyntick* > | > |--%46.85-- gic_handle_irq # 432 > | > |--%23.32-- context_tracking_user_exit # 215 > | > |--%22.34-- context_tracking_user_enter # 206 > | > |--%2.60-- SyS_execve # 24 > | > |--%1.30-- do_page_fault # 12 > | > |--%0.65-- SyS_write # 6 > | > |--%0.65-- schedule # 6 > | > |--%0.65-- SyS_nanosleep # 6 > | > |--%0.65-- syscall_trace_enter # 6 > | > |--%0.65-- SyS_faccessat # 6 > > %5.01 (14181) arm_stb_user_lo rcu_utilization #212 > | > --- *rcu_utilization* > | > |--%96.23-- gic_handle_irq # 204 > | > |--%1.89-- SyS_nanosleep # 4 > | > |--%0.94-- SyS_exit_group # 2 > | > |--%0.94-- do_notify_resume # 2 > > %4.86 (14181) arm_stb_user_lo user_exit #206 > | > --- *user_exit* > context_tracking_user_exit > > %4.86 (14181) arm_stb_user_lo context_tracking_user_exit #206 > | > --- context_tracking_user_exit > > %4.86 (14181) arm_stb_user_lo context_tracking_user_enter #206 > | > --- context_tracking_user_enter > > %4.86 (14181) arm_stb_user_lo user_enter #206 > | > --- *user_enter* > context_tracking_user_enter > > %2.95 (14181) arm_stb_user_lo gic_handle_irq #125 > | > --- gic_handle_irq > > > On Tue, Jun 30, 2020 at 9:45 AM Flavio Leitner <f...@sysclose.org> wrote: > > > On Tue, Jun 02, 2020 at 12:56:51PM -0700, Vinay Gupta wrote: > > > Hi Flavio, > > > > > > Thanks for your reply. > > > I have captured the suggested information but do not see anything that > > > could cause the packet drops. > > > Can you please take a look at the below data and see if you can find > > > something unusual ? > > > The PMDs are running on CPU 1,2,3,4 and CPU 1-7 are isolated cores. > > > > > > > > --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > > > root@bcm958802a8046c:~# cstats ; sleep 10; cycles > > > pmd thread numa_id 0 core_id 1: > > > idle cycles: 99140849 (7.93%) > > > processing cycles: 1151423715 (92.07%) > > > avg cycles per packet: 116.94 (1250564564/10693918) > > > avg processing cycles per packet: 107.67 (1151423715/10693918) > > > pmd thread numa_id 0 core_id 2: > > > idle cycles: 118373662 (9.47%) > > > processing cycles: 1132193442 (90.53%) > > > avg cycles per packet: 124.39 (1250567104/10053309) > > > avg processing cycles per packet: 112.62 (1132193442/10053309) > > > pmd thread numa_id 0 core_id 3: > > > idle cycles: 53805933 (4.30%) > > > processing cycles: 1196762002 (95.70%) > > > avg cycles per packet: 107.35 (1250567935/11649948) > > > avg processing cycles per packet: 102.73 (1196762002/11649948) > > > pmd thread numa_id 0 core_id 4: > > > idle cycles: 189102938 (15.12%) > > > processing cycles: 1061463293 (84.88%) > > > avg cycles per packet: 143.47 (1250566231/8716828) > > > avg processing cycles per packet: 121.77 (1061463293/8716828) > > > pmd thread numa_id 0 core_id 5: > > > pmd thread numa_id 0 core_id 6: > > > pmd thread numa_id 0 core_id 7: > > > > > > The core_id 3 is high loaded, and then it's more likely to show > > the drop issue when some other event happens. > > > > I think you need to run perf as I recommended before and see if > > there are context switches happening and why they are happening. > > > > If a context switch happens, it's either because the core is not > > well isolated or some other thing is going on. It will help to > > understand why the queue wasn't serviced for a certain amount of > > time. > > > > The issue is that running perf might introduce some load, so you > > will need adjust the traffic rate accordingly. > > > > HTH, > > fbl > > > > > > > > > > > > > > > *Runtime summary* comm parent sched-in > > > run-time min-run avg-run max-run stddev migrations > > > (count) (msec) (msec) > > > (msec) (msec) % > > > > > --------------------------------------------------------------------------------------------------------------------- > > > ksoftirqd/0[7] 2 1 0.079 0.079 > > > 0.079 0.079 0.00 0 > > > rcu_sched[8] 2 14 0.067 0.002 > > > 0.004 0.009 9.96 0 > > > rcuos/4[38] 2 6 0.027 0.002 > > > 0.004 0.008 20.97 0 > > > rcuos/5[45] 2 4 0.018 0.004 > > > 0.004 0.005 6.63 0 > > > kworker/0:1[71] 2 12 0.156 0.008 > > > 0.013 0.019 6.72 0 > > > mmcqd/0[1230] 2 3 0.054 0.001 > > > 0.018 0.031 47.29 0 > > > kworker/0:1H[1248] 2 1 0.006 0.006 > > > 0.006 0.006 0.00 0 > > > kworker/u16:2[1547] 2 16 0.045 0.001 > > > 0.002 0.012 26.19 0 > > > ntpd[5282] 1 1 0.063 0.063 > > > 0.063 0.063 0.00 0 > > > watchdog[6988] 1 2 0.089 0.012 > > > 0.044 0.076 72.26 0 > > > ovs-vswitchd[9239] 1 2 0.326 0.152 > > > 0.163 0.173 6.45 0 > > > revalidator8[9309/9239] 9239 2 1.260 0.607 > > > 0.630 0.652 3.58 0 > > > perf[27150] 27140 1 0.000 0.000 > > > 0.000 0.000 0.00 0 > > > > > > Terminated tasks: > > > sleep[27151] 27150 4 1.002 0.015 > > > 0.250 0.677 58.22 0 > > > > > > Idle stats: > > > CPU 0 idle for 999.814 msec ( 99.84%) > > > > > > > > > > > > *CPU 1 idle entire time window CPU 2 idle entire time window > > CPU 3 > > > idle entire time window CPU 4 idle entire time window* > > > CPU 5 idle for 500.326 msec ( 49.96%) > > > CPU 6 idle entire time window > > > CPU 7 idle entire time window > > > > > > Total number of unique tasks: 14 > > > Total number of context switches: 115 > > > Total run time (msec): 3.198 > > > Total scheduling time (msec): 1001.425 (x 8) > > > (END) > > > > > > > > > > > > *02:16:22 UID TGID TID %usr %system %guest %wait > > > %CPU CPU Command *02:16:23 0 9239 - 100.00 > > 0.00 > > > 0.00 0.00 100.00 5 ovs-vswitchd > > > 02:16:23 0 - 9239 2.00 0.00 0.00 0.00 > > > 2.00 5 |__ovs-vswitchd > > > 02:16:23 0 - 9240 0.00 0.00 0.00 0.00 > > > 0.00 0 |__vfio-sync > > > 02:16:23 0 - 9241 0.00 0.00 0.00 0.00 > > > 0.00 5 |__eal-intr-thread > > > 02:16:23 0 - 9242 0.00 0.00 0.00 0.00 > > > 0.00 5 |__dpdk_watchdog1 > > > 02:16:23 0 - 9244 0.00 0.00 0.00 0.00 > > > 0.00 5 |__urcu2 > > > 02:16:23 0 - 9279 0.00 0.00 0.00 0.00 > > > 0.00 5 |__ct_clean3 > > > 02:16:23 0 - 9308 0.00 0.00 0.00 0.00 > > > 0.00 5 |__handler9 > > > 02:16:23 0 - 9309 0.00 0.00 0.00 0.00 > > > 0.00 5 |__revalidator8 > > > 02:16:23 0 - 9328 0.00 0.00 0.00 0.00 > > > 0.00 6 |__pmd13 > > > 02:16:23 0 - 9330 100.00 0.00 0.00 0.00 > > > 100.00 3 |__pmd12 > > > 02:16:23 0 - 9331 100.00 0.00 0.00 0.00 > > > 100.00 1 |__pmd11 > > > 02:16:23 0 - 9332 0.00 0.00 0.00 0.00 > > > 0.00 7 |__pmd10 > > > 02:16:23 0 - 9333 0.00 0.00 0.00 0.00 > > > 0.00 5 |__pmd16 > > > 02:16:23 0 - 9334 100.00 0.00 0.00 0.00 > > > 100.00 2 |__pmd15 > > > 02:16:23 0 - 9335 100.00 0.00 0.00 0.00 > > > 100.00 4 |__pmd14 > > > > > --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > > > > > > Thanks > > > Vinay > > > > > > On Tue, Jun 2, 2020 at 12:06 PM Flavio Leitner <f...@sysclose.org> wrote: > > > > > > > On Mon, Jun 01, 2020 at 07:27:09PM -0400, Shahaji Bhosle via dev wrote: > > > > > Hi Ben/Ilya, > > > > > Hope you guys are doing well and staying safe. I have been chasing a > > > > weird > > > > > problem with small drops and I think that is causing lots of TCP > > > > > retransmission. > > > > > > > > > > Setup details > > > > > iPerf3(1k-5K > > > > > Servers)<--DPDK2:OvS+DPDK(VxLAN:BOND)[DPDK0+DPDK1)<====2x25G<==== > > > > > [DPDK0+DPDK1)(VxLAN:BOND)OVS+DPDKDPDK2<---iPerf3(Clients) > > > > > > > > > > All the Drops are ring drops on BONDed functions on the server > > side. I > > > > > have 4 CPUs each with 3PMD threads, DPDK0, DPDK1 and DPDK2 all > > running > > > > with > > > > > 4 Rx rings each. > > > > > > > > > > What is interesting is when I give each Rx rings its own CPU the > > drops go > > > > > away. Or if I set cother_config:emc-insert-inv-prob=1 the drops go > > away. > > > > > But I need to scale up the number of flows so trying to run this > > with EMC > > > > > disabled. > > > > > > > > > > I can tell that the rings are not getting serviced for 30-40usec > > because > > > > of > > > > > some kind context switch or interrupts on these cores. I have tried > > to do > > > > > the usual isolation, nohz_full rcu_nocbs etc. Move all the interrupts > > > > away > > > > > from these cores etc. But nothing helps. I mean it improves, but the > > > > drops > > > > > still happen. > > > > > > > > When you disable the EMC (or reduce its efficiency) the per packet cost > > > > increases, then it becomes more sensitive to variations. If you share > > > > a CPU with multiple queues, you decrease the amount of time available > > > > to process the queue. In either case, there will be less room to > > tolerate > > > > variations. > > > > > > > > Well, you might want to use 'perf' and monitor for the scheduling > > events > > > > and then based on the stack trace see what is causing it and try to > > > > prevent it. > > > > > > > > For example: > > > > # perf record -e sched:sched_switch -a -g sleep 1 > > > > > > > > For instance, you might see that another NIC used for management has > > > > IRQs assigned to one isolated CPU. You can move it to another CPU to > > > > reduce the noise, etc... > > > > > > > > Another suggestion is look at PMD thread idle statistics because it > > > > will tell you how much "extra" room you have left. As it approaches > > > > to 0, more fine tuned your setup needs to be to avoid drops. > > > > > > > > HTH, > > > > -- > > > > fbl > > > > > > > > -- > > fbl > > -- fbl _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev