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Message-ID: <7a7e1e21-df3d-4623-d9cd-51f5272919d5@arm.com>
Date:   Mon, 28 Mar 2022 11:24:16 +0200
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Subject: Re: [PATCH 0/6] Add latency_nice priority
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To:     Vincent Guittot <vincent.guittot@linaro.org>, 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
Cc:     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,
        dhaval.giani@oracle.com, qperret@google.com,
        tim.c.chen@linux.intel.com
References: <20220311161406.23497-1-vincent.guittot@linaro.org>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
In-Reply-To: <20220311161406.23497-1-vincent.guittot@linaro.org>
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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.