linux-kernel - Re: [PATCH] sched/core: add forced idle accounting for cgroups

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Date:   Fri, 20 May 2022 08:43:47 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Cruz Zhao <CruzZhao@...ux.alibaba.com>
Subject: Re: [PATCH] sched/core: add forced idle accounting for cgroups

Hello,

Sorry about late reply and thanks for the ping. I missed this one.

On Fri, May 13, 2022 at 12:23:16PM -0700, Josh Don wrote:
> Yea, that's right, this doesn't require the cpu controller to be
> enabled. Are you suggesting to add a new field to cgroup_base_stat?

Yes, that's what I meant. I think it'd fit there better.

> One other weird artifact of collecting forceidle time is that a cpu
> may account it on behalf of its hyperthread sibling. Currently, the
> core rstat code always accounts to the current cpu's percpu rstat
> field. I can add an accounting function to support writes to a
> different cpu's field, in order to make sure that the per-cpu totals
> are correct (the forceidle accounting code holds rq->__lock, which
> protects all HT siblings of a core). percpu totals aren't currently
> exported in cgroup v2, but this is useful information that we'll
> consume, so it would be nice to keep it accurate.

Sure, as long as it doesn't incur overhead when not used.

Thanks.

-- 
tejun