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

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Date:   Sat, 5 Nov 2022 14:28:43 +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 09:13, Joel Fernandes wrote:

> > If I have a task that has p->latency_nice = 20 but it belongs to a cgroup
> > that has tg->cpu.latency.nice = -19
> 
> Just for the task placement signal, One way is to go through the se hierarchy
> till the root and get the minimum. Then make that the effective value. So In
> your example that would make it -19 so prefer idle = 1.  We should need
> a Boolean signal. Not pretty but not the end of the world imho.

It is not hard to hack something. My worry is about consistency; and
maintainers in the future saying that doesn't fit the current design.

I'd love for this to be usable everywhere as-is. That requires the expectations
for both users and consumers are being made clear from the beginning.

What I was asking for is for the documentation to reflect this, and the
implementation of this effective function being made available from the start.


Cheers

--
Qais Yousef