From: Juri Lelli <juri.lelli@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
dietmar.eggemann@arm.com, luca.abeni@santannapisa.it,
bristot@redhat.com, balsini@android.com, dvyukov@google.com,
tglx@linutronix.de, vpillai@digitalocean.com,
rostedt@goodmis.org
Subject: Re: [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs pick_next_task
Date: Mon, 29 Jul 2019 15:17:01 +0200 [thread overview]
Message-ID: <20190729131701.GB8927@localhost.localdomain> (raw)
In-Reply-To: <20190729130438.GE31398@hirez.programming.kicks-ass.net>
On 29/07/19 15:04, Peter Zijlstra wrote:
> On Mon, Jul 29, 2019 at 01:27:02PM +0200, Juri Lelli wrote:
> > On 29/07/19 13:15, Peter Zijlstra wrote:
> > > 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.
> >
> > Right. But, I was wondering about the __schedule()->pick_next_task()
> > case, where, say, prev (rq->curr) is RT/CFS and next (p) is DEADLINE.
>
> So we do pick_next_task() first and then set rq->curr (obviously). So
> the first set_next_task() will see rq->curr != p and we'll do the push
> balance stuff.
>
> Then the above pattern will always see rq->curr == p and we'll not
> trigger push balancing.
>
> Now, looking at it, this also doesn't do push balancing when we
> re-select the same task, even though we really should be doing it. So I
> suppose not adding the condition, and always doing the push balance,
> while wasteful, is not wrong.
Right, also because deadline_queue_push_tasks() already checks if there
are tasks to potentially push around before queuing the balance
callback.
next prev parent reply other threads:[~2019-07-29 13:17 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 14:54 [RFC][PATCH 00/13] SCHED_DEADLINE server infrastructure Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 01/13] sched/deadline: Impose global limits on sched_attr::sched_period Peter Zijlstra
2019-07-29 8:57 ` Juri Lelli
2019-07-29 11:45 ` Daniel Bristot de Oliveira
2019-08-02 17:21 ` Alessio Balsini
2019-08-05 11:53 ` Peter Zijlstra
2019-08-22 12:29 ` Alessio Balsini
2019-08-22 16:51 ` Peter Zijlstra
2019-08-31 14:41 ` Alessio Balsini
2019-09-02 9:16 ` Peter Zijlstra
2019-09-02 12:31 ` Peter Zijlstra
2019-09-04 10:16 ` Steven Rostedt
2019-09-04 11:30 ` Peter Zijlstra
2019-09-04 13:24 ` Joel Fernandes
2019-09-04 14:11 ` Will Deacon
2019-09-04 14:35 ` Joel Fernandes
2019-09-04 15:52 ` Peter Zijlstra
2019-10-23 17:17 ` [PATCH 4.4 4.9 4.14] loop: Add LOOP_SET_DIRECT_IO to compat ioctl Alessio Balsini
2019-10-23 17:22 ` Alessio Balsini
2019-10-25 0:17 ` Sasha Levin
2020-05-20 18:38 ` [RFC][PATCH 01/13] sched/deadline: Impose global limits on sched_attr::sched_period Juri Lelli
2020-05-21 13:45 ` Daniel Bristot de Oliveira
2020-06-16 12:21 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 02/13] stop_machine: Fix stop_cpus_in_progress ordering Peter Zijlstra
2019-07-30 13:16 ` Phil Auld
2019-07-30 13:22 ` Steven Rostedt
2019-07-26 14:54 ` [RFC][PATCH 03/13] sched: Fix kerneldoc comment for ia64_set_curr_task Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Peter Zijlstra
2019-07-29 9:25 ` Juri Lelli
2019-07-29 11:15 ` Peter Zijlstra
2019-07-29 11:27 ` Juri Lelli
2019-07-29 13:04 ` Peter Zijlstra
2019-07-29 13:17 ` Juri Lelli [this message]
2019-07-29 14:40 ` Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 05/13] sched: Add task_struct pointer to sched_class::set_curr_task Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 06/13] sched/fair: Export newidle_balance() Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 07/13] sched: Allow put_prev_task() to drop rq->lock Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 08/13] sched: Rework pick_next_task() slow-path Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 09/13] sched: Unify runtime accounting across classes Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 10/13] sched/deadline: Collect sched_dl_entity initialization Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 11/13] sched/deadline: Move bandwidth accounting into {en,de}queue_dl_entity Peter Zijlstra
2019-07-26 14:54 ` [RFC][PATCH 12/13] sched/deadline: Introduce deadline servers Peter Zijlstra
2019-08-07 16:31 ` Dietmar Eggemann
2019-08-08 6:52 ` Juri Lelli
2019-08-08 7:52 ` Dietmar Eggemann
2019-08-08 7:56 ` Peter Zijlstra
2019-08-08 8:11 ` Dietmar Eggemann
2019-08-08 8:46 ` Juri Lelli
2019-08-08 8:57 ` Dietmar Eggemann
2019-08-08 9:27 ` Juri Lelli
2019-08-08 9:45 ` Juri Lelli
2019-08-30 11:24 ` Peter Zijlstra
2019-09-06 9:36 ` Juri Lelli
2019-08-08 10:31 ` Peter Zijlstra
2019-08-09 7:13 ` Juri Lelli
2019-08-08 6:59 ` Juri Lelli
2019-08-09 9:17 ` Dietmar Eggemann
2019-08-09 12:16 ` Juri Lelli
2019-07-26 14:54 ` [RFC][PATCH 13/13] sched/fair: Add trivial fair server Peter Zijlstra
2019-07-26 20:01 ` [RFC][PATCH 00/13] SCHED_DEADLINE server infrastructure luca abeni
2019-09-03 14:27 ` Alessio Balsini
2019-09-04 10:50 ` Juri Lelli
2019-09-04 11:32 ` Peter Zijlstra
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