Messages in this thread | | | Date | Fri, 19 Aug 2016 13:29:41 +0800 | From | Aaron Lu <> | Subject | Re: [LKP] [lkp] [sctp] a6c2f79287: netperf.Throughput_Mbps -37.2% regression |
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On Thu, Aug 18, 2016 at 08:45:42PM +0800, Xin Long wrote: > >> Hi, Aaron > >> > >> 1) > >> I talked with Marcelo about this one. > >> He said it might be related with cacheline. the new field distroyed > >> the prior cacheline. So on top of commit 826d253d57b1, pls only add > >> + unsigned long prsctp_param; > >> > >> to the end of struct sctp_chunk, then try. > > > > This doesn't work. > > > > If it's because of cache lines changed, I'm not sure this, either. > Maybe 2) is a good way to fix it.
A comparison of the good commit 826d253d57b1 and the bad a6c2f792873a:
tests: 8 testcase/path_params/tbox_group/run: netperf/ipv4-300s-200%-cs-localhost-10K-SCTP_STREAM_MANY-performance/lkp-ivb-d02
826d253d57b11f69 a6c2f792873aff332a4689717c ---------------- -------------------------- %stddev change %stddev \ | \ 3923 -37% 2461 netperf.Throughput_Mbps 9 -78% 2 vmstat.procs.r 112616 19% 133981 vmstat.system.cs 4053 7% 4350 vmstat.system.in 8598 ± 4% 957% 90912 softirqs.SCHED 16466114 -37% 10305467 softirqs.NET_RX 605899 -46% 329262 softirqs.TIMER 72067 ± 10% -63% 26356 ± 3% softirqs.RCU 4785 ± 7% -9% 4352 slabinfo.anon_vma_chain.num_objs 642 ± 7% 14% 731 ± 6% slabinfo.kmalloc-512.active_objs 4993 15% 5735 slabinfo.kmalloc-64.active_objs 4993 15% 5735 slabinfo.kmalloc-64.num_objs 2529 ± 4% -15% 2150 proc-vmstat.nr_alloc_batch 4.733e+08 -37% 2.999e+08 proc-vmstat.pgalloc_normal 8.476e+08 -37% 5.36e+08 proc-vmstat.pgfree 3.742e+08 -37% 2.361e+08 proc-vmstat.pgalloc_dma32 1.48e+08 -37% 93033641 proc-vmstat.numa_hit 1.48e+08 -37% 93033640 proc-vmstat.numa_local 0.05 ± 17% 52102% 24.80 turbostat.CPU%c1 0.64 3065% 20.10 ± 3% turbostat.CPU%c6 0.12 ± 39% 1900% 2.35 ± 3% turbostat.Pkg%pc2 0.46 ± 10% 1686% 8.22 ± 6% turbostat.Pkg%pc6 37.54 -14% 32.11 turbostat.PkgWatt 20.20 -25% 15.22 turbostat.CorWatt 99.31 -45% 54.97 turbostat.%Busy 3269 -45% 1803 turbostat.Avg_MHz 76510 ± 46% 3e+05% 1.954e+08 cpuidle.C1-IVB.time 19769 ± 17% 5534% 1113742 ± 5% cpuidle.C1E-IVB.time 151 ± 11% 4175% 6454 ± 7% cpuidle.C1E-IVB.usage 114 ± 14% 6216% 7232 ± 5% cpuidle.C3-IVB.usage 33074 ± 14% 5159% 1739419 ± 3% cpuidle.C3-IVB.time 8874 4203% 381901 cpuidle.C6-IVB.usage 8006184 4072% 3.34e+08 cpuidle.C6-IVB.time 12019 ± 35% 303% 48398 perf-stat.cpu-migrations 34232822 19% 40780053 perf-stat.context-switches 339045 5% 354573 perf-stat.minor-faults 339041 5% 354568 perf-stat.page-faults 2.776e+11 -28% 2.003e+11 perf-stat.branch-instructions 1.505e+12 -29% 1.065e+12 perf-stat.instructions 6.421e+11 -30% 4.473e+11 perf-stat.dTLB-loads 5.32e+11 -34% 3.536e+11 perf-stat.dTLB-stores 1.173e+11 -38% 7.271e+10 perf-stat.cache-references 3.735e+08 ± 5% -48% 1.959e+08 ± 4% perf-stat.iTLB-load-misses 3.864e+09 -51% 1.9e+09 perf-stat.branch-misses 4.069e+09 ± 20% -56% 1.798e+09 ± 40% perf-stat.dTLB-load-misses 5.285e+08 ± 22% -70% 1.585e+08 ± 16% perf-stat.dTLB-store-misses 7.126e+09 ± 16% -97% 2.27e+08 ± 4% perf-stat.cache-misses
The obvious change is: 1 the bad commit has a much fewer runnable process - vmstat.procs.r 2 the context switches are much higher in the bad commit - vmstat.system.cs
It all suggests the netperf processes go to sleep for some reason in the bad commit.
I used "perf record -p one_netperf_pid -e probe:pick_next_task_idle" as suggested by Tim to see where it went to sleep:
Samples: 78 of event 'probe:pick_next_task_idle', Event count(approx.): 78 Children Self Trace output ■- 100.00% 100.00% (ffffffff810fc750) ▒ __sendmsg_nocancel ▒ entry_SYSCALL_64_fastpath ▒ sys_sendmsg ▒ __sys_sendmsg ▒ ___sys_sendmsg ▒ inet_sendmsg ▒ sctp_sendmsg ▒ sctp_wait_for_sndbuf ▒ schedule_timeout ▒ schedule ▒ pick_next_task_idle
It doesn't look insane and sctp_wait_for_sndbuf may actually have something to do with a larger sctp_chunk I suppose?
The same perf record doesn't capture any sample for the good commit, which suggests the nerperf process doesn't sleep in sctp_wait_for_sndbuf.
Regards, Aaron
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