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SubjectRe: [lkp-robot] [sched/fair] d519329f72: unixbench.score -9.9% regression
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.

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?

> 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?

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".

> 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?

> 8611715 -58.9% 3537314 ± 3% unixbench.time.voluntary_context_switches
> 6639375 -9.1% 6033775 unixbench.workload

What the above metric represents?

> 26025 +3849.3% 1027825 interrupts.CAL:Function_call_interrupts

What this metric represents?

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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