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

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Date:   Mon, 28 Mar 2022 11:24:16 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, 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
Cc:     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,
        dhaval.giani@...cle.com, qperret@...gle.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH 0/6] Add latency_nice priority

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.