From: Valentin Schneider <valentin.schneider@arm.com>
To: Oliver Sang <oliver.sang@intel.com>
Cc: 0day robot <lkp@intel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, ying.huang@intel.com, feng.tang@intel.com,
zhengjun.xing@intel.com,
Lingutla Chandrasekhar <clingutla@codeaurora.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
Quentin Perret <qperret@google.com>,
Pavan Kondeti <pkondeti@codeaurora.org>,
Rik van Riel <riel@surriel.com>,
aubrey.li@linux.intel.com, yu.c.chen@intel.com
Subject: Re: [sched/fair] 38ac256d1c: stress-ng.vm-segv.ops_per_sec -13.8% regression
Date: Wed, 21 Apr 2021 11:27:49 +0100 [thread overview]
Message-ID: <87bla8ue3e.mognet@arm.com> (raw)
In-Reply-To: <20210421032022.GA13430@xsang-OptiPlex-9020>
Hi,
On 21/04/21 11:20, Oliver Sang wrote:
> hi, Valentin Schneider,
>
> On Wed, Apr 14, 2021 at 06:17:38PM +0100, Valentin Schneider wrote:
>> On 14/04/21 13:21, kernel test robot wrote:
>> > Greeting,
>> >
>> > FYI, we noticed a -13.8% regression of stress-ng.vm-segv.ops_per_sec due to commit:
>> >
>> >
>> > commit: 38ac256d1c3e6b5155071ed7ba87db50a40a4b58 ("[PATCH v5 1/3] sched/fair: Ignore percpu threads for imbalance pulls")
>> > url: https://github.com/0day-ci/linux/commits/Valentin-Schneider/sched-fair-load-balance-vs-capacity-margins/20210408-060830
>> > base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git 0a2b65c03e9b47493e1442bf9c84badc60d9bffb
>> >
>> > in testcase: stress-ng
>> > on test machine: 96 threads Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 192G memory
>> > with following parameters:
>> >
>> > nr_threads: 10%
>> > disk: 1HDD
>> > testtime: 60s
>> > fs: ext4
>> > class: os
>> > test: vm-segv
>> > cpufreq_governor: performance
>> > ucode: 0x5003006
>> >
>> >
>>
>> That's almost exactly the same result as [1], which is somewhat annoying
>> for me because I wasn't able to reproduce those results back then. Save
>> from scrounging the exact same machine to try this out, I'm not sure what's
>> the best way forward. I guess I can re-run the workload on whatever
>> machines I have and try to spot any potentially problematic pattern in the
>> trace...
>
> what's the machine model you used upon which the regression cannot be reproduced?
> we could check if we have similar model then re-check on the our machine.
>
I tested this on:
o Ampere eMAG (arm64, 32 cores)
o 2-socket Xeon E5-2690 (x86, 40 cores)
and found at worse a -0.3% regression and at best a 2% improvement. I know
that x86 box is somewhat ancient, but it's been my go-to "have I broken
x86?" test victim for a while :-)
> BTW, we supplied perf data in original report, not sure if they are helpful?
> or do you have suggestion which kind of data will be more helpful to you?
> we will continuously improve our report based on suggestions from community.
> Thanks a lot!
>
Staring at it some more, I notice a huge uptick in:
- major page faults (+315.2% and +270%)
- cache misses (+125.2% and +131.0%)
I don't really get the page faults; the cache misses I could somewhat
understand: this is adding p->flags and (p->set_child_tid)->flags accesses,
which are in different cachelines than p->se and p->cpus_mask used in
can_migrate_task().
I think I could dig some more into this with perf, but I'd need to be able
to reproduce this locally first...
>>
>> [1]: http://lore.kernel.org/r/20210223023004.GB25487@xsang-OptiPlex-9020
next prev parent reply other threads:[~2021-04-21 10:28 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-07 22:06 [PATCH v5 0/3] sched/fair: load-balance vs capacity margins Valentin Schneider
2021-04-07 22:06 ` [PATCH v5 1/3] sched/fair: Ignore percpu threads for imbalance pulls Valentin Schneider
2021-04-09 11:24 ` [tip: sched/core] " tip-bot2 for Lingutla Chandrasekhar
2021-04-09 12:05 ` tip-bot2 for Lingutla Chandrasekhar
2021-04-09 16:14 ` tip-bot2 for Lingutla Chandrasekhar
2021-04-14 5:21 ` [sched/fair] 38ac256d1c: stress-ng.vm-segv.ops_per_sec -13.8% regression kernel test robot
2021-04-14 17:17 ` Valentin Schneider
2021-04-21 3:20 ` Oliver Sang
2021-04-21 10:27 ` Valentin Schneider [this message]
2021-04-21 12:03 ` Peter Zijlstra
2021-04-22 7:47 ` Oliver Sang
2021-04-22 9:55 ` Valentin Schneider
2021-04-22 20:42 ` Valentin Schneider
2021-04-28 22:00 ` Valentin Schneider
2021-05-06 16:11 ` Valentin Schneider
2021-04-07 22:06 ` [PATCH v5 2/3] sched/fair: Clean up active balance nr_balance_failed trickery Valentin Schneider
2021-04-09 11:24 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2021-04-09 12:05 ` tip-bot2 for Valentin Schneider
2021-04-09 16:14 ` tip-bot2 for Valentin Schneider
2021-04-07 22:06 ` [PATCH v5 3/3] sched/fair: Introduce a CPU capacity comparison helper Valentin Schneider
2021-04-09 11:24 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2021-04-09 12:05 ` tip-bot2 for Valentin Schneider
2021-04-09 16:14 ` tip-bot2 for Valentin Schneider
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