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Date: Fri, 26 Apr 2024 13:16:07 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <efault@gmx.de>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>, mingo@redhat.com,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
	mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
	linux-kernel@vger.kernel.org, wuyun.abel@bytedance.com,
	tglx@linutronix.de, Chen Yu <yu.c.chen@intel.com>,
	Oliver Sang <oliver.sang@intel.com>
Subject: Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue
Message-ID: <20240426111607.GL12673@noisy.programming.kicks-ass.net>
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In-Reply-To: <20240426105607.GK12673@noisy.programming.kicks-ass.net>

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