linux-kernel - Re: [PATCH v7 6/9] sched/fair: Add sched group latency support

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Date:   Sat, 5 Nov 2022 13:41:36 +0000
From:   Qais Yousef <qyousef@...alina.io>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
        qais.yousef@....com, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, tj@...nel.org, qperret@...gle.com,
        tim.c.chen@...ux.intel.com, joshdon@...gle.com, timj@....org,
        kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org
Subject: Re: [PATCH v7 6/9] sched/fair: Add sched group latency support

On 11/04/22 14:57, Joel Fernandes wrote:

> > The current use of latency_nice doesn't need to walk the hierarchy
> > because it applies at each scheduling level so the childs
> > automatically follow parents' latency.
> 
> Not really, I don't see how that will work that way in the wake up path. The
> wake up path (EAS in particular) does not walk through CPU controller group
> hierarchy from top level, it only cares about cpuset/affinities and the
> "effective" values of tasks.
> 
> So when you wake up a task, how will you retrieve the attribute for 'prefer
> idle' in the wakeup path using this patchset? The only way is to aggregate
> the CGroup hierarchy information to get a per-task effective value; say using
> a min function.
> 
> If you see uclamp_rq_util_with(), that also is using doing uclamp
> aggregation similarly.
> 
> So I think Qais is asking about the aggregation function in the EAS wakeup
> path.

Yes that's what I was trying to say. Thanks for helping to clarify it!


Thanks

--
Qais Yousef