linux-kernel - Re: [PATCH 1/2] sched/rt: Fix RT utilization tracking during policy change

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Date:   Mon, 21 Jun 2021 10:03:13 +0100
From:   Vincent Donnefort <vincent.donnefort@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/rt: Fix RT utilization tracking during policy
 change

[...]

> >         /*
> > -        * If we are already running, then there's nothing
> > -        * that needs to be done. But if we are not running
> > -        * we may need to preempt the current running task.
> > -        * If that current running task is also an RT task
> > +        * If we are not running we may need to preempt the current
> > +        * running task. If that current running task is also an RT task
> >          * then see if we can move to another run queue.
> >          */
> >         if (task_on_rq_queued(p) && rq->curr != p) {
> > @@ -2355,6 +2353,13 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
> >                 if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq)))
> >                         resched_curr(rq);
> >         }
> > +
> > +       /*
> > +        * If we are running, update the avg_rt tracking, as the running time
> > +        * will now on be accounted into the latter.
> > +        */
> > +       if (task_current(rq, p))
> 
> task_current(rq,p) equals the "rq->curr != p" above. Having 2
> different ways to get the same value in the function is a bit
> confusing.
> 
> And call it once
> 
> Otherwise, the fix looks good to me

I can change it to something like:

if (task_current(rq, p)) {
    update_rt_rq_load_avg()
    return;
}

if (task_on_rq_queued(p) {
        ...
	if (p->prio ...)
		resched_curr(rq);
}

?

> 
> > +               update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);
> >  }
> >
> >  /*
> > --
> > 2.7.4
> >