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SubjectRe: [LKP] [lkp-robot] [mm] e27be240df: will-it-scale.per_process_ops -27.2% regression
On Wed, May 09, 2018 at 10:32:11AM +0800, Aaron Lu wrote:
> On Tue, May 08, 2018 at 01:26:40PM -0400, Johannes Weiner wrote:
> > Hello,
> >
> > On Tue, May 08, 2018 at 01:34:51PM +0800, kernel test robot wrote:
> > > FYI, we noticed a -27.2% regression of will-it-scale.per_process_ops due to commit:
> > >
> > >
> > > commit: e27be240df53f1a20c659168e722b5d9f16cc7f4 ("mm: memcg: make sure memory.events is uptodate when waking pollers")
> > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> > >
> > > in testcase: will-it-scale
> > > on test machine: 72 threads Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz with 128G memory
> > > with following parameters:
> > >
> > > nr_task: 100%
> > > mode: process
> > > test: page_fault3
> > > cpufreq_governor: performance
> > >
> > > 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
> >
> > This is surprising. Do you run these tests in a memory cgroup with a
> > limit set? Can you dump that cgroup's memory.events after the run?
>
> There is no cgroup related setup so yes, this is surprising.
> But the result is quite stable, I have just confirmed on another
> Haswell-EP machine.
>
> perf shows increased cycles spent for lock_page_memcg and
> unlock_page_memcg, maybe this can shed some light. Full profile for this
> commit and its parent are attached.
>
> I have also attached dmesg for both commits in case they are useful,
> please feel free to let me know if you need any other information. We
> also collected a ton of other information during the run like
> /proc/vmstat, /proc/meminfo, /proc/interrupt etc.

Test on Broadwell-EP also showed 35% regression, here are a list of
functions that take more CPU cycles with this commit according to perf:

a38c015f3156895b e27be240df53f1a20c659168e7
---------------- --------------------------
%stddev %change %stddev
\ | \
58033709 -35.0% 37727244 will-it-scale.workload
... ...
3.82 +6.1 9.97 perf-profile.self.cycles-pp.handle_mm_fault
3.19 +6.2 9.37 perf-profile.self.cycles-pp.page_remove_rmap
0.25 +6.5 6.71 perf-profile.self.cycles-pp.__unlock_page_memcg
3.63 +7.5 11.15 perf-profile.self.cycles-pp.page_add_file_rmap
0.60 +8.1 8.70 perf-profile.self.cycles-pp.lock_page_memcg

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