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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Mon, 28 Mar 2022 14:56:06 +0200
Message-ID: <CAKfTPtC36OLqrQ57bnGDi93N+3Ozk5cX-+KHHTWHkwCGp=z4gA@mail.gmail.com>
Subject: Re: [PATCH 0/6] Add latency_nice priority
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        linux-kernel@vger.kernel.org, parth@linux.ibm.com,
        qais.yousef@arm.com, chris.hyser@oracle.com,
        pkondeti@codeaurora.org, Valentin.Schneider@arm.com,
        patrick.bellasi@matbug.net, David.Laight@aculab.com,
        pjt@google.com, pavel@ucw.cz, tj@kernel.org, qperret@google.com,
        tim.c.chen@linux.intel.com
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Hi Dietmar,


On Mon, 28 Mar 2022 at 11:24, Dietmar Eggemann <dietmar.eggemann@arm.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