linux-kernel - Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue

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Date: Fri, 26 Apr 2024 13:16:07 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mike Galbraith <efault@....de>
Cc: K Prateek Nayak <kprateek.nayak@....com>, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
	linux-kernel@...r.kernel.org, wuyun.abel@...edance.com,
	tglx@...utronix.de, Chen Yu <yu.c.chen@...el.com>,
	Oliver Sang <oliver.sang@...el.com>
Subject: Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue

On Fri, Apr 26, 2024 at 12:56:07PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 25, 2024 at 01:28:55PM +0200, Peter Zijlstra wrote:
> > On Thu, Apr 18, 2024 at 06:24:59PM +0200, Mike Galbraith wrote:
> > > The root cause seems to be doing the delay dequeue business on
> > > exiting tasks. 
> > 
> > > ---
> > >  kernel/sched/fair.c |    5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -5374,6 +5374,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
> > >  		update_curr(cfs_rq);
> > > 
> > >  		if (sched_feat(DELAY_DEQUEUE) && sleep &&
> > > +		    !(entity_is_task(se) && (task_of(se)->flags & PF_EXITING)) &&
> > >  		    !entity_eligible(cfs_rq, se)) {
> > >  			if (cfs_rq->next == se)
> > >  				cfs_rq->next = NULL;
> > 
> > So I think this can be easier done in dequeue_task_fair(), where we
> > still know this is a task.
> > 
> > Perhaps something like (I'll test later):
> > 
> > 	if (p->flags & PF_EXITING)
> > 		flags &= ~DEQUEUE_SLEEP;
> > 
> > But now I need to go think about the case of removing a cgroup...
> > *urgh*.
> 
> I ended up with the below instead; lemme go run this unixbench spawn on it.

Seems to survive that.

I pushed out the patches with updates to queue/sched/eevdf