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From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Qais Yousef <qais.yousef@arm.com>
Cc:     linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Quentin Perret <qperret@google.com>,
        Pavan Kondeti <pkondeti@codeaurora.org>,
        Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH 0/8] sched/fair: misfit task load-balance tweaks
In-Reply-To: <66efcfb1-d6ee-248a-e337-d690cda1bb5a@arm.com>
References: <20210128183141.28097-1-valentin.schneider@arm.com> <20210203151400.ommltjjyuok4yj5e@e107158-lin> <jhjim792dro.mognet@arm.com> <66efcfb1-d6ee-248a-e337-d690cda1bb5a@arm.com>
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Date:   Thu, 04 Feb 2021 12:36:02 +0000
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On 04/02/21 13:03, Dietmar Eggemann wrote:
> How did you verify the benefit of these changes?
>
> It's clear that you need a platform with capacity_orig diffs <20%
> between CPU types (like Pixel4 - SD855 (4x261, 3x871, 1x1024) or QC's
> RB5 platform - SD865 (4x284, 3x871, 1*1024)) but which
> benchmark/testcase did you use?

Benchmark is the usual culprit:

  https://lisa-linux-integrated-system-analysis.readthedocs.io/en/master/kernel_tests.html#lisa.tests.scheduler.misfit.StaggeredFinishes

This test spawns 1 CPU hog per CPU, and screams whenever a CPU of capacity
X is running a hog while another CPU of capacity Y > X has been idling for
"too long" (a few ms). IOW it makes sure upmigration happens in a timely
manner.

Some of the test platforms (Juno (4+2 big.LITTLE), HiKey960 (4+4
big.LITTLE)) show some improvements due to the last 2 patches.

As for systems with CPUs in the [819-1024] "deadzone", Ionela's been kindly
running said test on said RB5, and the upmigrations look just fine with the
patches applied.