linux-kernel - Re: [PATCH 2/2] sched/fair: Relax task

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Date:   Mon, 19 Apr 2021 16:23:48 -0400
From:   Phil Auld <pauld@...hat.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Quentin Perret <qperret@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Lingutla Chandrasekhar <clingutla@...eaurora.org>
Subject: Re: [PATCH 2/2] sched/fair: Relax task_hot() for misfit tasks

On Mon, Apr 19, 2021 at 06:17:47PM +0100 Valentin Schneider wrote:
> On 19/04/21 08:59, Phil Auld wrote:
> > On Fri, Apr 16, 2021 at 10:43:38AM +0100 Valentin Schneider wrote:
> >> On 15/04/21 16:39, Rik van Riel wrote:
> >> > On Thu, 2021-04-15 at 18:58 +0100, Valentin Schneider wrote:
> >> >> @@ -7672,6 +7698,15 @@ int can_migrate_task(struct task_struct *p,
> >> >> struct lb_env *env)
> >> >>      if (tsk_cache_hot == -1)
> >> >>              tsk_cache_hot = task_hot(p, env);
> >> >>
> >> >> +	/*
> >> >> +	 * On a (sane) asymmetric CPU capacity system, the increase in
> >> >> compute
> >> >> +	 * capacity should offset any potential performance hit caused
> >> >> by a
> >> >> +	 * migration.
> >> >> +	 */
> >> >> +	if ((env->dst_grp_type == group_has_spare) &&
> >> >> +	    !migrate_degrades_capacity(p, env))
> >> >> +		tsk_cache_hot = 0;
> >> >
> >> > ... I'm starting to wonder if we should not rename the
> >> > tsk_cache_hot variable to something else to make this
> >> > code more readable. Probably in another patch :)
> >> >
> >>
> >> I'd tend to agree, but naming is hard. "migration_harmful" ?
> >
> > I thought Rik meant tsk_cache_hot, for which I'd suggest at least
> > buying a vowel and putting an 'a' in there :)
> >
> 
> That's the one I was eyeing: s/tsk_cache_hot/migration_harmful/ or
> somesuch. Right now we're feeding it:
>

Fair enough, my bad, the migration part immediately drew me to
migrate_degrades_capacity().

> o migrate_degrades_locality()
> o task_hot()
> 
> and I'm adding another one, so that's 2/3 which don't actually care about
> cache hotness, but rather "does doing this migration degrade/improve
> $criterion?"
> 

prefer_no_migrate? 


Cheers,
Phil
--