linux-kernel - Re: [PATCH] sched/fair: use signed long when compute energy delta in eas

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Message-ID: <d017749a-697e-9cda-4940-df4cdbdd3a55@arm.com>
Date:   Tue, 13 Apr 2021 11:58:40 +0100
From:   Pierre Gondois <pierre.gondois@....com>
To:     Xuewen Yan <xuewen.yan94@...il.com>
Cc:     Dietmar Eggemann <Dietmar.Eggemann@....com>,
        Quentin Perret <qperret@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Ryan Y <xuewyan@...mail.com>
Subject: Re: [PATCH] sched/fair: use signed long when compute energy delta in
 eas

Hi,
> >
> > In fair.c:select_task_rq_fair(), if feec() returns a error (< 0), then
> > prev_cpu is selected. I think it's better to still let feec() signal
> > that something happened and let select_task_rq_fair() select prev_cpu by
> > itself.
> In fair.c:select_task_rq_fair(), when feec() returns a error (< 0),
> the new_cpu = find_idlest_cpu() or select_idle_sibling().
> In your patch, you should return prev_cpu instead of -1 if you want to
> select the prev_cpu.
Having a negative delta doesn't imply that prev_cpu is still available.
E.g.: If prev_cpu cannot receive the task (and is skipped), and a  
negative delta appears when evaluating the other CPUs. In such case  
feec() cannot select prev_cpu. dst_cpu must be selected by another function.

> > Are you planning to submit a V2 with the bail out mechanism ?
> Maybe it would be better if you submitted the V2 ? I just check the
> patch and raised some questions.

I m ok to send a V2. I will submit it once we agreed.

Regards