* Re: [PATCH] kernel/sched/rt: Add a rescheduling point
2017-01-24 14:40 [PATCH] kernel/sched/rt: Add a rescheduling point Sebastian Andrzej Siewior
@ 2017-01-24 14:43 ` Sebastian Andrzej Siewior
2017-01-24 15:17 ` Peter Zijlstra
2017-01-25 12:16 ` Peter Zijlstra
2017-01-30 11:57 ` [tip:sched/core] sched/rt: Add a missing " tip-bot for Sebastian Andrzej Siewior
2 siblings, 1 reply; 5+ messages in thread
From: Sebastian Andrzej Siewior @ 2017-01-24 14:43 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: Ingo Molnar, linux-kernel, tglx
On 2017-01-24 15:40:06 [+0100], To Peter Zijlstra wrote:
> Since the change in commit fd7a4bed1835 ("sched, rt: Convert
> switched_{from, to}_rt() / prio_changed_rt() to balance callbacks") we
> don't reschedule a task under certain circumstances:
|switched_to_dl()
|{
|…
| if (rq->curr != p) {
| #ifdef CONFIG_SMP
| if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
| queue_push_tasks(rq);
| #else
| if (dl_task(rq->curr))
| check_preempt_curr_dl(rq, p, 0);
| else
| resched_curr(rq);
| #endif
| }
| }
This looks like it asks for a similar change.
Sebastian
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] kernel/sched/rt: Add a rescheduling point
2017-01-24 14:43 ` Sebastian Andrzej Siewior
@ 2017-01-24 15:17 ` Peter Zijlstra
0 siblings, 0 replies; 5+ messages in thread
From: Peter Zijlstra @ 2017-01-24 15:17 UTC (permalink / raw)
To: Sebastian Andrzej Siewior; +Cc: Ingo Molnar, linux-kernel, tglx, Juri Lelli
On Tue, Jan 24, 2017 at 03:43:54PM +0100, Sebastian Andrzej Siewior wrote:
> On 2017-01-24 15:40:06 [+0100], To Peter Zijlstra wrote:
> > Since the change in commit fd7a4bed1835 ("sched, rt: Convert
> > switched_{from, to}_rt() / prio_changed_rt() to balance callbacks") we
> > don't reschedule a task under certain circumstances:
>
> |switched_to_dl()
> |{
> |…
> | if (rq->curr != p) {
> | #ifdef CONFIG_SMP
> | if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
> | queue_push_tasks(rq);
> | #else
> | if (dl_task(rq->curr))
> | check_preempt_curr_dl(rq, p, 0);
> | else
> | resched_curr(rq);
> | #endif
> | }
> | }
>
> This looks like it asks for a similar change.
Indeed.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] kernel/sched/rt: Add a rescheduling point
2017-01-24 14:40 [PATCH] kernel/sched/rt: Add a rescheduling point Sebastian Andrzej Siewior
2017-01-24 14:43 ` Sebastian Andrzej Siewior
@ 2017-01-25 12:16 ` Peter Zijlstra
2017-01-30 11:57 ` [tip:sched/core] sched/rt: Add a missing " tip-bot for Sebastian Andrzej Siewior
2 siblings, 0 replies; 5+ messages in thread
From: Peter Zijlstra @ 2017-01-25 12:16 UTC (permalink / raw)
To: Sebastian Andrzej Siewior; +Cc: Ingo Molnar, linux-kernel, tglx, Steven Rostedt
On Tue, Jan 24, 2017 at 03:40:06PM +0100, Sebastian Andrzej Siewior wrote:
> Since the change in commit fd7a4bed1835 ("sched, rt: Convert
> switched_{from, to}_rt() / prio_changed_rt() to balance callbacks") we
> don't reschedule a task under certain circumstances:
>
> Lets say taskA, SCHED_OTHER, is running on CPU0 (and it may run only on
> CPU0) and holds a PI lock. This task is removed from the CPU because it
> used up its time slice and another SCHED_OTHER task is running. TaskB on
> CPU1 runs at RT priority and asks for the lock owned by taskA. This
> results in a priority boost for taskA. TaskB goes to sleep until the
> lock has been made available. TaskA is already runable (but not active)
> so it receives no wake up.
> The reality now is that taskA gets on the CPU once the scheduler decides
> to remove the current task despite the fact that a high priority task is
> enqueued and waiting. This may take a long time.
> The desired behaviour is that CPU0 immediately reschedules after the
> priority boost which made taskA the task with the lowest priority.
>
> Fixes: fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() /
> prio_changed_rt() to balance callbacks")
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> kernel/sched/rt.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 88254be118b0..cdba8d58dbc5 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2198,10 +2198,10 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
> #ifdef CONFIG_SMP
> if (tsk_nr_cpus_allowed(p) > 1 && rq->rt.overloaded)
> queue_push_tasks(rq);
> -#else
> + else
I killed that "else" as well, because the queue_push_tasks() can fail to
actually push the task, in which case we'd still miss the preemption.
> +#endif /* CONFIG_SMP */
> if (p->prio < rq->curr->prio)
> resched_curr(rq);
> -#endif /* CONFIG_SMP */
> }
> }
>
> --
> 2.11.0
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip:sched/core] sched/rt: Add a missing rescheduling point
2017-01-24 14:40 [PATCH] kernel/sched/rt: Add a rescheduling point Sebastian Andrzej Siewior
2017-01-24 14:43 ` Sebastian Andrzej Siewior
2017-01-25 12:16 ` Peter Zijlstra
@ 2017-01-30 11:57 ` tip-bot for Sebastian Andrzej Siewior
2 siblings, 0 replies; 5+ messages in thread
From: tip-bot for Sebastian Andrzej Siewior @ 2017-01-30 11:57 UTC (permalink / raw)
To: linux-tip-commits
Cc: bigeasy, hpa, mingo, efault, torvalds, peterz, tglx, linux-kernel
Commit-ID: 619bd4a71874a8fd78eb6ccf9f272c5e98bcc7b7
Gitweb: http://git.kernel.org/tip/619bd4a71874a8fd78eb6ccf9f272c5e98bcc7b7
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Tue, 24 Jan 2017 15:40:06 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 30 Jan 2017 11:46:37 +0100
sched/rt: Add a missing rescheduling point
Since the change in commit:
fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks")
... we don't reschedule a task under certain circumstances:
Lets say task-A, SCHED_OTHER, is running on CPU0 (and it may run only on
CPU0) and holds a PI lock. This task is removed from the CPU because it
used up its time slice and another SCHED_OTHER task is running. Task-B on
CPU1 runs at RT priority and asks for the lock owned by task-A. This
results in a priority boost for task-A. Task-B goes to sleep until the
lock has been made available. Task-A is already runnable (but not active),
so it receives no wake up.
The reality now is that task-A gets on the CPU once the scheduler decides
to remove the current task despite the fact that a high priority task is
enqueued and waiting. This may take a long time.
The desired behaviour is that CPU0 immediately reschedules after the
priority boost which made task-A the task with the lowest priority.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() prio_changed_rt() to balance callbacks")
Link: http://lkml.kernel.org/r/20170124144006.29821-1-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/deadline.c | 3 +--
kernel/sched/rt.c | 3 +--
2 files changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 491ff66..27737f3 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1729,12 +1729,11 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
#ifdef CONFIG_SMP
if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
queue_push_tasks(rq);
-#else
+#endif
if (dl_task(rq->curr))
check_preempt_curr_dl(rq, p, 0);
else
resched_curr(rq);
-#endif
}
}
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 88254be..704f2b8 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2198,10 +2198,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
#ifdef CONFIG_SMP
if (tsk_nr_cpus_allowed(p) > 1 && rq->rt.overloaded)
queue_push_tasks(rq);
-#else
+#endif /* CONFIG_SMP */
if (p->prio < rq->curr->prio)
resched_curr(rq);
-#endif /* CONFIG_SMP */
}
}
^ permalink raw reply related [flat|nested] 5+ messages in thread