linux-kernel - Re: [PATCH v6 2/3] sched/fair: Add cfs bandwidth burst statistics

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Message-ID: <YNnm0bUfCmB54FYW@hirez.programming.kicks-ass.net>
Date:   Mon, 28 Jun 2021 17:12:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Huaixin Chang <changhuaixin@...ux.alibaba.com>
Cc:     luca.abeni@...tannapisa.it, anderson@...unc.edu, baruah@...tl.edu,
        bsegall@...gle.com, dietmar.eggemann@....com,
        dtcccc@...ux.alibaba.com, juri.lelli@...hat.com,
        khlebnikov@...dex-team.ru, linux-kernel@...r.kernel.org,
        mgorman@...e.de, mingo@...hat.com, odin@...d.al, odin@...dal.com,
        pauld@...head.com, pjt@...gle.com, rostedt@...dmis.org,
        shanpeic@...ux.alibaba.com, tj@...nel.org,
        tommaso.cucinotta@...tannapisa.it, vincent.guittot@...aro.org,
        xiyou.wangcong@...il.com
Subject: Re: [PATCH v6 2/3] sched/fair: Add cfs bandwidth burst statistics

On Mon, Jun 28, 2021 at 05:00:30PM +0200, Peter Zijlstra wrote:
> I was hoping we could get away with something simpler, like maybe:
> 
> 	u64 old_runtim = cfs_b->runtime;
> 
> 	cfs_b->runtime += cfs_b->quota
> 	cfs_b->runtime = min(cfs_b->runtime, cfs_b->quota + cfs_b->burst);
> 
> 	if (cfs_b->runtime - old_runtime > cfs_b->quota)
> 		cfs_b->nr_bursts++;
> 
> Would that be good enough?

Bah,, of course not ... :-/ At best we can detect == quota, which might
be a good enough indicator of burst.