linux-kernel - Re: [PATCH v4 3/3] sched/fair: Introduce a CPU capacity comparison helper

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Message-ID: <87h7kjo141.mognet@arm.com>
Date:   Tue, 06 Apr 2021 16:59:26 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org
Cc:     Qais Yousef <qais.yousef@....com>,
        Lingutla Chandrasekhar <clingutla@...eaurora.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Quentin Perret <qperret@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 3/3] sched/fair: Introduce a CPU capacity comparison helper

On 06/04/21 17:37, Dietmar Eggemann wrote:
> On 01/04/2021 21:30, Valentin Schneider wrote:
>> While at it, replace group_smaller_{min, max}_cpu_capacity() with
>> comparisons of the source group's min/max capacity and the destination
>> CPU's capacity.
>
> IMHO, you haven't mentioned why you replace local sched group with dst
> CPU. I can see that only the capacity of the dst CPU makes really sense
> here. Might be worth mentioning in the patch header why. There is some
> of it in v3 6/7 but that's a different change.
>

Right, some of it got lost in the shuffling. This was a separate change in
v1 (4/8). I can reuse that changelog into:

"""
Also note that comparing capacity extrema of local and source sched_group's
doesn't make much sense when at the day of the day the imbalance will be
pulled by a known env->dst_cpu, whose capacity can be anywhere within the
local group's capacity extrema.

While at it, replace group_smaller_{min, max}_cpu_capacity() with
comparisons of the source group's min/max capacity and the destination
CPU's capacity.
"""

> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
>
> [...]