Re: [signal] 4bad58ebc8: will-it-scale.per_thread_ops -3.3% regression

From: Oliver Sang
Date: Thu Apr 22 2021 - 01:45:02 EST

hi, Thomas Gleixner,

On Tue, Apr 20, 2021 at 08:35:06PM +0200, Thomas Gleixner wrote:
> On Tue, Apr 20 2021 at 11:08, kernel test robot wrote:
> > FYI, we noticed a -3.3% regression of will-it-scale.per_thread_ops due to commit:
> >
> > commit: 4bad58ebc8bc4f20d89cff95417c9b4674769709 ("signal: Allow tasks to cache one sigqueue struct")
> > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git sched/core
> >
> > in testcase: will-it-scale
> > on test machine: 192 threads Intel(R) Xeon(R) Platinum 9242 CPU @ 2.30GHz with 192G memory
> > with following parameters:
> >
> > nr_task: 100%
> > mode: thread
> > test: futex3
> > cpufreq_governor: performance
> > ucode: 0x5003006
> >
> > test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
> > test-url: https://github.com/antonblanchard/will-it-scale
> > commit:
> > 69995ebbb9 ("signal: Hand SIGQUEUE_PREALLOC flag to __sigqueue_alloc()")
> > 4bad58ebc8 ("signal: Allow tasks to cache one sigqueue struct")
> >
> > 69995ebbb9d37173 4bad58ebc8bc4f20d89cff95417
> > ---------------- ---------------------------
> > %stddev %change %stddev
> > \ | \
> > 1.273e+09 -3.3% 1.231e+09 will-it-scale.192.threads
> > 6630224 -3.3% 6409738 will-it-scale.per_thread_ops
> > 1.273e+09 -3.3% 1.231e+09 will-it-scale.workload
> > 1638 ± 3% -7.8% 1510 ± 5% sched_debug.cfs_rq:/.runnable_avg.max
> > 297.83 ± 68% +1747.6% 5502 ±152% interrupts.33:PCI-MSI.524291-edge.eth0-TxRx-2
> > 297.83 ± 68% +1747.6% 5502 ±152% interrupts.CPU12.33:PCI-MSI.524291-edge.eth0-TxRx-2
>
> This change is definitely not causing more network traffic
>
> > 8200 -33.4% 5459 ± 35% interrupts.CPU27.NMI:Non-maskable_interrupts
> > 8200 -33.4% 5459 ± 35% interrupts.CPU27.PMI:Performance_monitoring_interrupts
> > 8199 -33.4% 5459 ± 35% interrupts.CPU28.NMI:Non-maskable_interrupts
> > 8199 -33.4% 5459 ± 35% interrupts.CPU28.PMI:Performance_monitoring_interrupts
> > 6148 ± 33% -11.2% 5459 ± 35% interrupts.CPU29.NMI:Non-maskable_interrupts
> > 6148 ± 33% -11.2% 5459 ± 35% interrupts.CPU29.PMI:Performance_monitoring_interrupts
> > 4287 ± 8% +33.6% 5730 ± 15% interrupts.CPU49.CAL:Function_call_interrupts
> > 6356 ± 19% +49.6% 9509 ± 19% interrupts.CPU97.CAL:Function_call_interrupts
>
> Neither does it increase the number of function calls
>
> > 407730 ± 8% +37.5% 560565 ± 7% perf-stat.i.dTLB-load-misses
> > 415959 ± 8% +40.4% 583928 ± 7% perf-stat.ps.dTLB-load-misses
>
> And this massive increase does not make sense either.
>
> Confused.

FYI.
we re-test this, and confirmed the regression persistent. still:

69995ebbb9d37173 4bad58ebc8bc4f20d89cff95417
---------------- ---------------------------
%stddev %change %stddev
\ | \
1.271e+09 -3.3% 1.229e+09 will-it-scale.192.threads
6620228 -3.3% 6401749 will-it-scale.per_thread_ops
1.271e+09 -3.3% 1.229e+09 will-it-scale.workload

both fbc and parent use identical config, as attached in original report.

data for 4bad58ebc8bc4f20d89cff95417:
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json: "will-it-scale.per_thread_ops": [
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6404491,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6421116,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6402763,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6403483,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6412066,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6414511,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6395917, <------ new 14 runs
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6396872,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6400830,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6408883,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6403844,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6405911,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6390766,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6394523,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6394594,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6399547,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6402487,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6394673,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6400717,
4bad58ebc8bc4f20d89cff95417c9b4674769709/matrix.json- 6386997

data for parent (69995ebbb9d37173):
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json: "will-it-scale.per_thread_ops": [
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6640509,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6630326,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6633025,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6625355,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6623274,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6628858,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6614380, <----- new 14 runs
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6607324,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6613340,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6610083,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6616290,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6616934,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6618978,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6627108,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6609973,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6618440,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6617191,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6615858,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6615761,
69995ebbb9d3717306a165db88a1292b63f77a37/matrix.json- 6621558

>
> Thanks,
>
> tglx