linux-kernel - Re: [PATCH 0/6] sched,delayacct: Some cleanups

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Date:   Thu, 6 May 2021 08:29:40 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, mingo@...nel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, pbonzini@...hat.com, maz@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        riel@...riel.com, hannes@...xchg.org
Subject: Re: [PATCH 0/6] sched,delayacct: Some cleanups

On Wed, May 05, 2021 at 12:59:40PM +0200, Peter Zijlstra wrote:
> Hi,
> 
> Due to:
> 
>   https://lkml.kernel.org/r/0000000000001d43ac05c0f5c6a0@google.com
> 
> and general principle, delayacct really shouldn't be using ktime (pvclock also
> really shouldn't be doing what it does, but that's another story). This lead me
> to looking at the SCHED_INFO, SCHEDSTATS, DELAYACCT (and PSI) accounting hell.
> 
> The rest of the patches are an attempt at simplifying all that a little. All
> that crud is enabled by default for distros which is leading to a death by a
> thousand cuts.
> 
> The last patch is an attempt at default disabling DELAYACCT, because I don't
> think anybody actually uses that much, but what do I know, there were no ill
> effects on my testbox. Perhaps we should mirror
> /proc/sys/kernel/sched_schedstats and provide a delayacct sysctl for runtime
> frobbing.
>

There are tools like iotop that use delayacct to display information. When the
code was checked in, we did run SPEC* back in the day 2006 to find overheads,
nothing significant showed. Do we have any date on the overhead your seeing?

I'll look at the patches

Balbir Singh.