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

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Date:   Mon, 28 Mar 2022 14:56:06 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
        qais.yousef@....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
Subject: Re: [PATCH 0/6] Add latency_nice priority

Hi Dietmar,


On Mon, 28 Mar 2022 at 11:24, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 11/03/2022 17:14, Vincent Guittot wrote:
> > This patchset restarts the work about adding a latency nice priority to
> > describe the latency tolerance of cfs tasks.
> >
> > The patches [1-4] have been done by Parth:
> > https://lore.kernel.org/lkml/20200228090755.22829-1-parth@linux.ibm.com/
> >
> > I have just rebased and moved the set of latency priority outside the
> > priority update. I have removed the reviewed tag because the patches
> > are 2 years old.
> >
> > The patches [5-6] use latency nice priority to decide if a cfs task can
> > preempt the current running task. Patch 5 gives some tests results with
> > cyclictests and hackbench to highlight the benefit of latency nice
> > priority for short interactive task or long intensive tasks.
>
> The Android specific `latency_nice` (in Android `latency_sensitive`
> [latency_nice < 0]) use case `Skip energy aware task placement` favors
> an idle CPU over the EAS search path for a `latency_sensitive` task.
>
> https://lkml.kernel.org/r/2aa4b838-c298-ec7d-08f3-caa50cc87dc2@arm.com
>
> This is Android proprietary code similar to what we have in
> find_idlest_group_cpu() in mainline.
> We talked to the Android folks last week and IMHO they are not convinced
> that they can switch this to the proposed `latency_nice->tweak
> preemption` use case.

Thanks for discussing this with Android folks. It's not always easy to
change the behavior of a product and I would be interested to discuss
this with them. Sometimes you need a PoC to get convinced