linux-kernel - Re: [PATCH 07/15] sched/smp: Use lag to simplify cross-runqueue placement

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Date:   Wed, 13 Sep 2023 11:03:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     mingo@...nel.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, corbet@....net,
        qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, pjt@...gle.com, pavel@....cz,
        qperret@...gle.com, tim.c.chen@...ux.intel.com, joshdon@...gle.com,
        timj@....org, kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org, efault@....de,
        tglx@...utronix.de
Subject: Re: [PATCH 07/15] sched/smp: Use lag to simplify cross-runqueue
 placement

On Tue, Sep 12, 2023 at 05:32:21PM +0200, Sebastian Andrzej Siewior wrote:
> On 2023-05-31 13:58:46 [+0200], Peter Zijlstra wrote:
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -12492,22 +12440,9 @@ static void task_fork_fair(struct task_s
> >  
> >  	cfs_rq = task_cfs_rq(current);
> >  	curr = cfs_rq->curr;
> > -	if (curr) {
> > +	if (curr)
> >  		update_curr(cfs_rq);
> > -		se->vruntime = curr->vruntime;
> > -	}
> >  	place_entity(cfs_rq, se, 1);
> > -
> > -	if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) {
> 
> Since the removal of sysctl_sched_child_runs_first there is no user of
> this anymore. There is still the sysctl file sched_child_runs_first with
> no functionality.
> Is this intended or should it be removed?

Hurmph... I think that knob has been somewat dysfunctional for a long
while and it might be time to remove it.

Ingo?