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SubjectRe: [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs pick_next_task
On Mon, Jul 29, 2019 at 11:25:19AM +0200, Juri Lelli wrote:
> Hi,
>
> On 26/07/19 16:54, Peter Zijlstra wrote:
> > Because pick_next_task() implies set_curr_task() and some of the
> > details haven't matter too much, some of what _should_ be in
> > set_curr_task() ended up in pick_next_task, correct this.
> >
> > This prepares the way for a pick_next_task() variant that does not
> > affect the current state; allowing remote picking.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > kernel/sched/deadline.c | 23 ++++++++++++-----------
> > kernel/sched/rt.c | 27 ++++++++++++++-------------
> > 2 files changed, 26 insertions(+), 24 deletions(-)
> >
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -1694,12 +1694,21 @@ static void start_hrtick_dl(struct rq *r
> > }
> > #endif
> >
> > -static inline void set_next_task(struct rq *rq, struct task_struct *p)
> > +static void set_next_task_dl(struct rq *rq, struct task_struct *p)
> > {
> > p->se.exec_start = rq_clock_task(rq);
> >
> > /* You can't push away the running task */
> > dequeue_pushable_dl_task(rq, p);
> > +
> > + if (hrtick_enabled(rq))
> > + start_hrtick_dl(rq, p);
> > +
> > + if (rq->curr->sched_class != &dl_sched_class)
> > + update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
> > +
> > + if (rq->curr != p)
> > + deadline_queue_push_tasks(rq);
>
> It's a minor thing, but I was wondering why you added the check on curr.
> deadline_queue_push_tasks() already checks if are there pushable tasks,
> plus curr can still be of a different class at this point?

Hmm, so by moving that code into set_next_task() it is exposed to the:

if (queued)
deuque_task();
if (running)
put_prev_task();

/* do stuff */

if (queued)
enqueue_task();
if (running)
set_next_task();

patter from core.c; and in that case nothing changes. That said; I
might've gotten it wrong.

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