linux-kernel - Re: [PATCH -v2 15/17] sched: Fix migrate

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Message-ID: <20201012112824.GU2628@hirez.programming.kicks-ass.net>
Date:   Mon, 12 Oct 2020 13:28:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        bigeasy@...utronix.de, qais.yousef@....com, swood@...hat.com,
        valentin.schneider@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vincent.donnefort@....com, tj@...nel.org
Subject: Re: [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing

On Mon, Oct 12, 2020 at 11:56:09AM +0200, Dietmar Eggemann wrote:
> On 05/10/2020 16:57, Peter Zijlstra wrote:
> 
> [...]
> 
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -1859,7 +1859,7 @@ static struct task_struct *pick_next_pus
> >   * running task can migrate over to a CPU that is running a task
> >   * of lesser priority.
> >   */
> > -static int push_rt_task(struct rq *rq)
> > +static int push_rt_task(struct rq *rq, bool pull)
> >  {
> >  	struct task_struct *next_task;
> >  	struct rq *lowest_rq;
> > @@ -1873,6 +1873,34 @@ static int push_rt_task(struct rq *rq)
> >  		return 0;
> >  
> >  retry:
> > +	if (is_migration_disabled(next_task)) {
> > +		struct task_struct *push_task = NULL;
> > +		int cpu;
> > +
> > +		if (!pull || rq->push_busy)
> > +			return 0;
> 
> Shouldn't there be the same functionality in push_dl_task(), i.e.
> returning 0 earlier for a task with migration_disabled?

No, deadline didn't implement HAVE_RT_PUSH_IPI.