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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Mon, 27 Nov 2023 17:58:24 -0800
Message-ID: <CAJD7tkameJBrJQxRj+ibKL6-yd-i0wyoyv2cgZdh3ZepA1p7wA@mail.gmail.com>
Subject: Re: [PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg
To:     Oliver Sang <oliver.sang@intel.com>
Cc:     oe-lkp@lists.linux.dev, lkp@intel.com,
        Johannes Weiner <hannes@cmpxchg.org>,
        Domenico Cerasuolo <cerasuolodomenico@gmail.com>,
        cgroups@vger.kernel.org, linux-mm@kvack.org, ying.huang@intel.com,
        feng.tang@intel.com, fengwei.yin@intel.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Ivan Babrou <ivan@cloudflare.com>, Tejun Heo <tj@kernel.org>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Waiman Long <longman@redhat.com>, kernel-team@cloudflare.com,
        Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>,
        linux-kernel@vger.kernel.org
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On Mon, Nov 27, 2023 at 5:46=E2=80=AFPM Oliver Sang <oliver.sang@intel.com>=
 wrote:
>
> hi, Yosry Ahmed,
>
> On Mon, Nov 27, 2023 at 01:13:44PM -0800, Yosry Ahmed wrote:
> > On Wed, Nov 22, 2023 at 5:54=E2=80=AFAM kernel test robot <oliver.sang@=
intel.com> wrote:
> > >
> > >
> > >
> > > Hello,
> > >
> > > kernel test robot noticed a -30.2% regression of will-it-scale.per_th=
read_ops on:
> > >
> > >
> > > commit: c7fbfc7b4e089c4a9b292b1973a42a5761c1342f ("[PATCH v3 3/5] mm:=
 memcg: make stats flushing threshold per-memcg")
> > > url: https://github.com/intel-lab-lkp/linux/commits/Yosry-Ahmed/mm-me=
mcg-change-flush_next_time-to-flush_last_time/20231116-103300
> > > base: https://git.kernel.org/cgit/linux/kernel/git/akpm/mm.git mm-eve=
rything
> > > patch link: https://lore.kernel.org/all/20231116022411.2250072-4-yosr=
yahmed@google.com/
> > > patch subject: [PATCH v3 3/5] mm: memcg: make stats flushing threshol=
d per-memcg
> > >
> > > testcase: will-it-scale
> > > test machine: 104 threads 2 sockets (Skylake) with 192G memory
> > > parameters:
> > >
> > >         nr_task: 50%
> > >         mode: thread
> > >         test: fallocate2
> > >         cpufreq_governor: performance
> > >
> > >
> >
> > This regression was also reported in v2, and I explicitly mention it
> > in the cover letter here:
> > https://lore.kernel.org/lkml/20231116022411.2250072-1-yosryahmed@google=
.com/
>
> got it. this also reminds us to read cover letter for a patch set in the
> future. Thanks!
>
> >
> > In a nutshell, I think this microbenchmark regression does not
> > represent real workloads. On the other hand, there are demonstrated
> > benefits on real workloads from this series in terms of stats reading
> > time.
> >
>
> ok, if there are future versions of this patch, or when it is merged, we =
will
> ignore similar results.
>
> just a small question, since we focus on microbenchmark, if we found othe=
r
> regression (or improvement) on tests other than will-it-scale::fallocate,
> do you want us to send report or just ignore them, either?

I think it would be useful to know if there are
regressions/improvements in other microbenchmarks, at least to
investigate whether they represent real regressions.