linux-kernel - Re: [PATCH 13/23] sched,ion: Convert to sched_set

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Message-ID: <CAKfTPtBsFDt8JyxjD39B2YP+kCN9nXWZxnaJys9sz2CjWzd1Zw@mail.gmail.com>
Date:   Wed, 22 Apr 2020 15:36:22 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Qais Yousef <qais.yousef@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 13/23] sched,ion: Convert to sched_set_normal()

On Wed, 22 Apr 2020 at 15:29, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Apr 22, 2020 at 03:21:45PM +0200, Vincent Guittot wrote:
> > On Wed, 22 Apr 2020 at 13:29, Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > In an attempt to take away sched_setscheduler() from modules, change
> > > this into sched_set_normal(.nice = 19).
> > >
> > > Cc: john.stultz@...aro.org
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > Reviewed-by: Ingo Molnar <mingo@...nel.org>
> > > ---
> > >  drivers/staging/android/ion/ion_heap.c |    3 ---
> > >  1 file changed, 3 deletions(-)
> > >
> > > --- a/drivers/staging/android/ion/ion_heap.c
> > > +++ b/drivers/staging/android/ion/ion_heap.c
> > > @@ -244,8 +244,6 @@ static int ion_heap_deferred_free(void *
> > >
> > >  int ion_heap_init_deferred_free(struct ion_heap *heap)
> > >  {
> > > -       struct sched_param param = { .sched_priority = 0 };
> > > -
> > >         INIT_LIST_HEAD(&heap->free_list);
> > >         init_waitqueue_head(&heap->waitqueue);
> > >         heap->task = kthread_run(ion_heap_deferred_free, heap,
> > > @@ -255,7 +253,7 @@ int ion_heap_init_deferred_free(struct i
> > >                        __func__);
> > >                 return PTR_ERR_OR_ZERO(heap->task);
> > >         }
> > > -       sched_setscheduler(heap->task, SCHED_IDLE, &param);
> > > +       sched_set_normal(heap->task, 19);
> >
> > Would it make sense to have a sched_set_idle(task) to enable kernel
> > setting SCHED_IDLE task ?
> >
> > SCHED_NORMAL w/ nice 19 and SCHED_IDLE tasks are not treated in the
> > same way when checking for preemption at  wakeup
>
> Yeah, but does it really matter? I did indeed consider it, but got
> lazy. Is there a definite need for IDLE?

John is the best to answer this for this driver but SCHED_IDLE will
let other tasks which might be involved in end user interaction like
on Android to run first