linux-kernel - Re: [PATCH V2] sched/deadline: Update rq_clock of later

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Message-ID: <20180801224556.2d0b9342@vmware.local.home>
Date:   Wed, 1 Aug 2018 22:45:56 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH V2] sched/deadline: Update rq_clock of later_rq when
 pushing a task

On Mon, 16 Jul 2018 13:45:21 +0300
Kirill Tkhai <ktkhai@...tuozzo.com> wrote:

> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -2090,8 +2090,16 @@ 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().
> > +	 * Then, set ENQUEUE_NOCLOCK flag to avoid updating the rq_clock
> > +	 * again in the activate_task()->enqueue_task().  
> 
> Is the second sentence really needed? It seems everybody knows, what NOCLOCK
> flag does, and we does not have to paraphrase this in every place it's used :)

I would keep the mention, but change the comment:

	/*
	 * Update the later_rq clock before calling add_running_bw()
	 * because the clock is used by cpufreq_update_util() that is
	 * inside __add_running_bw(). As the later_rq clock is already
	 * updated, we need to set ENQUEUE_NOCLOCK to prevent
	 * activate_task() from updating it again.
	 */
Other than that...

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve


> 
> > +	 */
> > +	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);