From 619bd4a71874a8fd78eb6ccf9f272c5e98bcc7b7 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 24 Jan 2017 15:40:06 +0100 Subject: [PATCH] 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 Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Thomas Gleixner 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 --- 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 491ff663e1b6..27737f34757d 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 88254be118b0..704f2b89abf1 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 */ } } -- 2.20.1