linux-kernel - Re: [PATCH V3] sched/deadline: Update rq_clock of later

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Message-ID: <20180720125329.GD3642@localhost.localdomain>
Date:   Fri, 20 Jul 2018 14:53:29 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org, Clark Williams <williams@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH V3] sched/deadline: Update rq_clock of later_rq when
 pushing a task

On 20/07/18 14:48, Peter Zijlstra wrote:
> On Fri, Jul 20, 2018 at 02:46:15PM +0200, Peter Zijlstra wrote:
> > On Fri, Jul 20, 2018 at 11:16:30AM +0200, Daniel Bristot de Oliveira wrote:
> > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > > index fbfc3f1d368a..8b50eea4b607 100644
> > > --- a/kernel/sched/deadline.c
> > > +++ b/kernel/sched/deadline.c
> > > @@ -2090,8 +2090,14 @@ static int push_dl_task(struct rq *rq)
> > >  	sub_rq_bw(&next_task->dl, &rq->dl);
> > >  	set_task_cpu(next_task, later_rq->cpu);
> > >  	add_rq_bw(&next_task->dl, &later_rq->dl);
> > > +
> > > +	/*
> > > +	 * Update the later_rq clock here, because the clock is used
> > > +	 * by the cpufreq_update_util() inside __add_running_bw().
> > > +	 */
> > > +	update_rq_clock(later_rq);
> > >  	add_running_bw(&next_task->dl, &later_rq->dl);
> > > -	activate_task(later_rq, next_task, 0);
> > > +	activate_task(later_rq, next_task, ENQUEUE_NOCLOCK);
> > >  	ret = 1;
> > >  
> > >  	resched_curr(later_rq);
> > 
> > Why isn't push_rt_task() affected by the very same issue?
> 
> Aah, I see, its the add_running_bw() think; for which RT doesn't have a
> counter-part.

Right, but doesn't enqueue_top_rt_rq end-up being called by activate_
task on lowest_rq? Mmm.