linux-kernel - Re: [PATCH RT 5/8] sched/deadline: Reclaim cpuset bandwidth in .migrate_task

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Message-ID: <20191001085209.GA6481@localhost.localdomain>
Date:   Tue, 1 Oct 2019 10:52:09 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Scott Wood <swood@...hat.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT 5/8] sched/deadline: Reclaim cpuset bandwidth in
 .migrate_task_rq()

On 30/09/19 11:24, Scott Wood wrote:
> On Mon, 2019-09-30 at 09:12 +0200, Juri Lelli wrote:

[...]

> > Hummm, I was actually more worried about the fact that we call free_old_
> > cpuset_bw_dl() only if p->state != TASK_WAKING.
> 
> Oh, right. :-P  Not sure what I had in mind there; we want to call it
> regardless.
> 
> I assume we need rq->lock in free_old_cpuset_bw_dl()?  So something like

I think we can do with rcu_read_lock_sched() (see dl_task_can_attach()).

> this:
> 
> 	if (p->state == TASK_WAITING)
> 		raw_spin_lock(&rq->lock);
> 	free_old_cpuset_bw_dl(rq, p);
> 	if (p->state != TASK_WAITING)
> 		return;
> 
> 	if (p->dl.dl_non_contending) {
> 	....	
> 
> BTW, is the full cpumask_intersects() necessary or would it suffice to see
> that the new cpu is not in the old span?

Checking new cpu only should be OK.

Thanks,

Juri