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SubjectRe: [lkp-robot] [sched/fair] d519329f72: unixbench.score -9.9% regression
On 04/03, Patrick Bellasi wrote:
>Hi Xiaolong,
>
>On 02-Apr 11:20, kernel test robot wrote:
>>
>> Greeting,
>>
>> FYI, we noticed a -9.9% regression of unixbench.score due to commit:
>
>thanks for the report, I'll try to reproduce it locally to better
>understand what's going on.

Thanks for your attention and feedback.

>
>Meanwhile, I'm a little puzzled about some of the following
>numbers... likely looking at the code it should be more clear.
>But, maybe someone already knows the response.
>
>> commit: d519329f72a6f36bc4f2b85452640cfe583b4f81 ("sched/fair: Update util_est only on util_avg updates")
>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>
>To give a bit of context, this patch is the last of a small series
>introducing util_est:
> https://lkml.org/lkml/2018/3/9/245
>where we actually enable it by turning of by default the corresponding SCHED_FEAT.
>Thus, all the effect of util_est are visible just after this very last patch.
>
>I'm not surprised that, if there are issues related to util_est, they
>manifest at this stage.
>
>> in testcase: unixbench
>> on test machine: 8 threads Intel(R) Core(TM) i7 CPU 870 @ 2.93GHz with 6G memory
>> with following parameters:
>>
>> runtime: 300s
>> nr_task: 100%
>> test: execl
>>
>> test-description: UnixBench is the original BYTE UNIX benchmark suite aims to test performance of Unix-like system.
>> test-url: https://github.com/kdlucas/byte-unixbench
>
>AFAIU, this benchmark is composed of 12 different test cases:
> https://github.com/intel/lkp-tests/blob/master/jobs/unixbench.yaml
>and it's reporting a regression for "only" 1 of those tests (execl).
>
>Is that correct?

Yes, this regression is only regarding to the execl test in unixbench.

>
>> Details are as below:
>> -------------------------------------------------------------------------------------------------->
>>
>>
>> To reproduce:
>>
>> git clone https://github.com/intel/lkp-tests.git
>> cd lkp-tests
>> bin/lkp install job.yaml # job file is attached in this email
>> bin/lkp run job.yaml
>
>Will try to give it a run in the next days.
>
>>
>> =========================================================================================
>> compiler/kconfig/nr_task/rootfs/runtime/tbox_group/test/testcase:
>> gcc-7/x86_64-rhel-7.2/100%/debian-x86_64-2016-08-31.cgz/300s/nhm-white/execl/unixbench
>>
>> commit:
>> a07630b8b2 ("sched/cpufreq/schedutil: Use util_est for OPP selection")
>> d519329f72 ("sched/fair: Update util_est only on util_avg updates")
>>
>> a07630b8b2c16f82 d519329f72a6f36bc4f2b85452
>> ---------------- --------------------------
>> %stddev %change %stddev
>> \ | \
>> 4626 -9.9% 4167 unixbench.score
>
>Is this overall score a composition of the following scores?
>

Actually, the unixbench.score the main performance indicator of unixbench, it is
obtained directly from the raw output of unixbench as below:

------------------------------------------------------------------------
Benchmark Run: Sat Mar 31 2018 08:51:09 - 08:56:48
8 CPUs in system; running 8 parallel copies of tests

Execl Throughput 17946.9 lps (30.0 s, 7 samples)

System Benchmarks Partial Index BASELINE RESULT INDEX
Execl Throughput 43.0 17946.9 4173.7
========
System Benchmarks Index Score (Partial Only) 4173.7


>In general, it would be nice to see in the following metrics which one
>is considered "the lower the better" or "the higher the better".

It's a good suggestion, we'll work to make this metrics change more readable.

>
>> 3495362 ± 4% +70.4% 5957769 ± 2% unixbench.time.involuntary_context_switches
>
>The above seems to indicate an increase in contention which generated
>scheduler enforced context switches. But, AFAIU, the test under
>analysis generates just one single task which keep execl itself.
>I can't see how util_est can this generated an increase in context
>switches? Will investigate better.
>
>> 2.866e+08 -11.6% 2.534e+08 unixbench.time.minor_page_faults
>> 666.75 -9.7% 602.25 unixbench.time.percent_of_cpu_this_job_got
>> 1830 -9.7% 1653 unixbench.time.system_time
>> 395.13 -5.2% 374.58 unixbench.time.user_time
>
>When I read "system_time" and "user_time" I'm expecting it to be a
>"the lower the better" metric.
>Thus, if that's the case, by just looking at these last two metrics:
>doesn't that means that the test is actually completing faster with
>util_est enabled?

It seems so.

>
>> 8611715 -58.9% 3537314 ± 3% unixbench.time.voluntary_context_switches
>> 6639375 -9.1% 6033775 unixbench.workload
>
>What the above metric represents?

unixbench.time.voluntary_context_switches is obtained through time (GNU time 1.7), we use
it to record the time metrics while benchmark running, the whole output is like:

Command being timed: "/lkp/lkp/src/tests/unixbench"
User time (seconds): 377.38
System time (seconds): 1664.25
Percent of CPU this job got: 601%
Elapsed (wall clock) time (h:mm:ss or m:ss): 5:39.39
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 8956
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 255131129
Voluntary context switches: 3520290
Involuntary context switches: 6137488
Swaps: 0
File system inputs: 0
File system outputs: 0
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0

unixbench.workload is defined as the total operations in unixbench for
all processes/threads.

>
>> 26025 +3849.3% 1027825 interrupts.CAL:Function_call_interrupts
>
>What this metric represents?

This metric is obtain through /proc/interrupts, we would take snapshot of this
file before and after the test, then sum up the Function call interrupts for
all cpus during the test.

Thanks,
Xiaolong
>
>This is a big variation which I cannot easily see as related to
>util_est overheads... unless these are interrupts related to tasks
>migrations, which potentially can affect LB and WKP code paths.
>
>> 4856 ± 14% -27.4% 3523 ± 11% slabinfo.filp.active_objs
>> 3534356 -8.8% 3223918 softirqs.RCU
>> 77929 -11.2% 69172 vmstat.system.cs
>> 19489 ± 2% +7.5% 20956 vmstat.system.in
>> 9.05 ± 9% +11.0% 10.05 ± 8% boot-time.dhcp
>> 131.63 ± 4% +8.6% 142.89 ± 7% boot-time.idle
>> 9.07 ± 9% +11.0% 10.07 ± 8% boot-time.kernel_boot
>> 76288 ± 3% -12.8% 66560 ± 3% meminfo.DirectMap4k
>> 16606 -13.1% 14433 meminfo.Inactive
>> 16515 -13.2% 14341 meminfo.Inactive(anon)
>> 11.87 ± 5% +7.8 19.63 ± 4% mpstat.cpu.idle%
>> 0.07 ± 35% -0.0 0.04 ± 17% mpstat.cpu.soft%
>> 68.91 -6.1 62.82 mpstat.cpu.sys%
>
>The following:
>
>> 29291570 +325.4% 1.246e+08 cpuidle.C1.time
>> 8629105 -36.1% 5513780 cpuidle.C1.usage
>> 668733 ± 12% +11215.3% 75668902 ± 2% cpuidle.C1E.time
>> 9763 ± 12% +16572.7% 1627882 ± 2% cpuidle.C1E.usage
>> 1.834e+08 ± 9% +23.1% 2.258e+08 ± 11% cpuidle.C3.time
>> 222674 ± 8% +133.4% 519690 ± 6% cpuidle.C3.usage
>
>are other really big variations which metrics represents, AFAIU, the
>following IDLE states:
>- C1 : Core doesn't work, clocks stopped
>- C1E : Core doesn't work, clocks stopped and voltage lowered
>- C3 : L1 and L2 copied to L3, all core clocks stopped
>
>Thus, it seems to me that, with the patches in, we are more likely to
>sleep longer. Which suggests a more aggressive race-to-idle policy:
>running at higher frequencies to complete faster and sleep
>longer and deeper.
>
>This would kind-of match with the idea of completing faster, but I'm
>not completely sure... however, if that should be the case, again I
>would say that's a benefit, not a regression.
>
>
>> 4129 -13.3% 3581 proc-vmstat.nr_inactive_anon
>> 4129 -13.3% 3581 proc-vmstat.nr_zone_inactive_anon
>> 2.333e+08 -12.2% 2.049e+08 proc-vmstat.numa_hit
>> 2.333e+08 -12.2% 2.049e+08 proc-vmstat.numa_local
>> 6625 -10.9% 5905 proc-vmstat.pgactivate
>> 2.392e+08 -12.1% 2.102e+08 proc-vmstat.pgalloc_normal
>> 2.936e+08 -12.6% 2.566e+08 proc-vmstat.pgfault
>> 2.392e+08 -12.1% 2.102e+08 proc-vmstat.pgfree
>
>All the following metrics:
>
>> 2850 -15.3% 2413 turbostat.Avg_MHz
>> 8629013 -36.1% 5513569 turbostat.C1
>> 1.09 +3.5 4.61 turbostat.C1%
>> 9751 ± 12% +16593.0% 1627864 ± 2% turbostat.C1E
>> 0.03 ± 19% +2.8 2.80 turbostat.C1E%
>> 222574 ± 8% +133.4% 519558 ± 6% turbostat.C3
>> 6.84 ± 8% +1.5 8.34 ± 10% turbostat.C3%
>> 2.82 ± 7% +250.3% 9.87 ± 2% turbostat.CPU%c1
>> 6552773 ± 3% +23.8% 8111699 ± 2% turbostat.IRQ
>> 2.02 ± 11% +28.3% 2.58 ± 9% turbostat.Pkg%pc3
>
>maybe they can help to understand better what's going on with respect
>to the race-to-idle theory...
>
>
>> 7.635e+11 -12.5% 6.682e+11 perf-stat.branch-instructions
>> 3.881e+10 -12.9% 3.381e+10 perf-stat.branch-misses
>> 2.09 -0.3 1.77 ± 4% perf-stat.cache-miss-rate%
>> 1.551e+09 -15.1% 1.316e+09 ± 4% perf-stat.cache-misses
>> 26177920 -10.5% 23428188 perf-stat.context-switches
>> 1.99 -2.8% 1.93 perf-stat.cpi
>> 7.553e+12 -14.7% 6.446e+12 perf-stat.cpu-cycles
>
>This:
>
>> 522523 ± 2% +628.3% 3805664 perf-stat.cpu-migrations
>
>is another good point. With util_est we are affecting LB and WKP
>paths... but, give the specific execl test, not entirely sure how we
>can affect migrations using util_est.
>
>Have to check better these two points:
>- do we reset PELT after an execl?
>- do we trigger a possible task migration after and execl
>
>
>> 2.425e+10 ± 4% -14.3% 2.078e+10 perf-stat.dTLB-load-misses
>> 1.487e+12 -11.3% 1.319e+12 perf-stat.dTLB-loads
>> 1.156e+10 ± 3% -7.7% 1.066e+10 perf-stat.dTLB-store-misses
>> 6.657e+11 -11.1% 5.915e+11 perf-stat.dTLB-stores
>> 0.15 +0.0 0.15 perf-stat.iTLB-load-miss-rate%
>> 5.807e+09 -11.0% 5.166e+09 perf-stat.iTLB-load-misses
>> 3.799e+12 -12.1% 3.34e+12 perf-stat.iTLB-loads
>> 3.803e+12 -12.2% 3.338e+12 perf-stat.instructions
>> 654.99 -1.4% 646.07 perf-stat.instructions-per-iTLB-miss
>> 0.50 +2.8% 0.52 perf-stat.ipc
>> 2.754e+08 -11.6% 2.435e+08 perf-stat.minor-faults
>> 1.198e+08 ± 7% +73.1% 2.074e+08 ± 4% perf-stat.node-stores
>> 2.754e+08 -11.6% 2.435e+08 perf-stat.page-faults
>> 572928 -3.4% 553258 perf-stat.path-length
>>
>>
>>
>> unixbench.score
>>
>> 4800 +-+------------------------------------------------------------------+
>> |+ + + |
>> 4700 +-+ + + :+ +. :+ + + |
>> | + + + +. : + + + + + + + .+++++ .+ +|
>> 4600 +-+ +++ :+++ + ++: : :+ +++ ++.++++ + ++++ ++ |
>> | + + + ++ ++ + |
>> 4500 +-+ |
>> | |
>> 4400 +-+ |
>> | |
>> 4300 +-+ |
>> O |
>> 4200 +-O O O OOOO OO OOO OOOO OOOO O O |
>> |O OO OOOOO O O OO O O O O O OO |
>> 4100 +-+------------------------------------------------------------------+
>>
>>
>> unixbench.workload
>>
>> 9e+06 +-+---------------------------------------------------------------+
>> | : |
>> 8.5e+06 +-+ : |
>> | : |
>> 8e+06 +-+ : |
>> | :: |
>> 7.5e+06 +-+ : : + |
>> | +: : : + |
>> 7e+06 +-+ + + :: : :: + + : + + + + + |
>> |:+ + + : :: : : :: : :+ : : ::+ :+ .+ :+ ++ ++ + ++ ::++|
>> 6.5e+06 +-O+ +++ ++++ +++ + ++ +.+ + ++ + + + + + + + +.+++ + |
>> O O O O O O O |
>> 6e+06 +O+OOO O OOOOOOOO OOOO OO OOOOOOOOO O O O OO |
>> | O |
>> 5.5e+06 +-+---------------------------------------------------------------+
>>
>>
>>
>> [*] bisect-good sample
>> [O] bisect-bad sample
>>
>>
>>
>> Disclaimer:
>> Results have been estimated based on internal Intel analysis and are provided
>> for informational purposes only. Any difference in system hardware or software
>> design or configuration may affect actual performance.
>>
>>
>> Thanks,
>> Xiaolong
>
>[...]
>
>> #
>> # CPU Frequency scaling
>> #
>> CONFIG_CPU_FREQ=y
>> CONFIG_CPU_FREQ_GOV_ATTR_SET=y
>> CONFIG_CPU_FREQ_GOV_COMMON=y
>> # CONFIG_CPU_FREQ_STAT is not set
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set
>
>The governor in use is not schedutil... thus util_est could effect the
>test just because of signals tracking overheads, of because of the way
>we affect tasks placement in WK and LB paths... which can be
>correlated to the impact on task migrations and preemption...
>
>> CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set
>> # CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL is not set
>> CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
>> CONFIG_CPU_FREQ_GOV_POWERSAVE=y
>> CONFIG_CPU_FREQ_GOV_USERSPACE=y
>> CONFIG_CPU_FREQ_GOV_ONDEMAND=y
>> CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
>> # CONFIG_CPU_FREQ_GOV_SCHEDUTIL is not set
>>
>> #
>> # CPU frequency scaling drivers
>> #
>> CONFIG_X86_INTEL_PSTATE=y
>> CONFIG_X86_PCC_CPUFREQ=m
>> CONFIG_X86_ACPI_CPUFREQ=m
>> CONFIG_X86_ACPI_CPUFREQ_CPB=y
>> CONFIG_X86_POWERNOW_K8=m
>> CONFIG_X86_AMD_FREQ_SENSITIVITY=m
>> # CONFIG_X86_SPEEDSTEP_CENTRINO is not set
>> CONFIG_X86_P4_CLOCKMOD=m
>>
>
>--
>#include <best/regards.h>
>
>Patrick Bellasi

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