linux-kernel - Re: [PATCH 0/6] Add latency

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Date:   Sat, 9 Apr 2022 13:28:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
        chris.hyser@...cle.com, pkondeti@...eaurora.org,
        Valentin.Schneider@....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,
        Wei Wang <wvw@...gle.com>
Subject: Re: [PATCH 0/6] Add latency_nice priority

On Sat, 9 Apr 2022 18:08:41 +0100
Qais Yousef <qais.yousef@....com> wrote:

> One other corner case to consider if you're working on next version is what
> should happen when there are multiple tasks of the same priority on the rq. RT
> scheduler will push/pull tasks to ensure the task will get to run ASAP if
> there's another cpu at lower priority is available. Seems a lot of complexity
> to add to CFS, but at the same time if 2 important tasks require low latency
> are on the same rq, one of them will suffer without introducing the ability to
> migrate one of them where it can get to run sooner.

Instead of having the greedy algorithm of the RT push/pull logic, how
hard would it be to have the load balancer know of these tasks, and try
to keep them on different CPUs? When two are queued on the same CPU,
could it be possible to just trigger load balancing and let it do the
work?

-- Steve