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References: <20231116022411.2250072-4-yosryahmed@google.com> <202311221542.973f16ad-oliver.sang@intel.com>
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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Mon, 27 Nov 2023 13:13:44 -0800
Message-ID: <CAJD7tkYnn6CxSJdo0QJ1hc6cFY_qWLuJ0=S6g_Pm=GBV+Ss-jw@mail.gmail.com>
Subject: Re: [PATCH v3 3/5] mm: memcg: make stats flushing threshold per-memcg
To:     kernel test robot <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 Wed, Nov 22, 2023 at 5:54=E2=80=AFAM kernel test robot <oliver.sang@inte=
l.com> wrote:
>
>
>
> Hello,
>
> kernel test robot noticed a -30.2% regression of will-it-scale.per_thread=
_ops on:
>
>
> commit: c7fbfc7b4e089c4a9b292b1973a42a5761c1342f ("[PATCH v3 3/5] mm: mem=
cg: make stats flushing threshold per-memcg")
> url: https://github.com/intel-lab-lkp/linux/commits/Yosry-Ahmed/mm-memcg-=
change-flush_next_time-to-flush_last_time/20231116-103300
> base: https://git.kernel.org/cgit/linux/kernel/git/akpm/mm.git mm-everyth=
ing
> patch link: https://lore.kernel.org/all/20231116022411.2250072-4-yosryahm=
ed@google.com/
> patch subject: [PATCH v3 3/5] mm: memcg: make stats flushing threshold pe=
r-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=
/

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.