linux-kernel - Re: [memcg] a8c49af3be: hackbench.throughput -13.7% regression

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Message-ID: <CALvZod4CZt6oSdyC1xZzWOj2nDCdhk0Qn6Ux1UjNmH9Oe7ukrg@mail.gmail.com>
Date:   Tue, 26 Apr 2022 22:08:36 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Yin Fengwei <fengwei.yin@...el.com>,
        kernel test robot <oliver.sang@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        kernel test robot <lkp@...el.com>,
        Ying <ying.huang@...el.com>, Feng Tang <feng.tang@...el.com>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Subject: Re: [memcg] a8c49af3be: hackbench.throughput -13.7% regression

On Tue, Apr 26, 2022 at 9:34 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
[...]
>
> The only seemingly expensive operation in the mod_memcg_state() path
> is the call to cgroup_rstat_updated() (through memcg_rstat_updated()).
> One idea off the top of my head is to batch calls to
> cgroup_rstat_updated(), similar to what 11192d9c124d ("memcg: flush
> stats only if updated") did on the flush side. I am interested to see
> what memcg maintainers think about this problem (and the proposed
> solution).
>

I am suspecting this is some code alignment changes which is causing
this difference. Let's first confirm the issue before thinking about
the optimizations.