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sched/core: Fix pick_next_task() for RT,DL 

Pavan noticed that the following commit:

  49ee576809 ("sched/core: Optimize pick_next_task() for idle_sched_class")

... broke RT,DL balancing by robbing them of the opportinty to do new-'idle'
balancing when their last runnable task (on that runqueue) goes away.

Reported-by: Pavan Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: 49ee576809 ("sched/core: Optimize pick_next_task() for idle_sched_class")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Peter Zijlstra 2017-03-01 10:51:47 +01:00 committed by Ingo Molnar
parent 4c77b18cf8
commit 0ba87bb27d
1 changed files with 8 additions and 3 deletions
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11
kernel/sched/core.c
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@ -3273,10 +3273,15 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct task_struct *p;
/*
* Optimization: we know that if all tasks are in
* the fair class we can call that function directly:
* Optimization: we know that if all tasks are in the fair class we can
* call that function directly, but only if the @prev task wasn't of a
* higher scheduling class, because otherwise those loose the
* opportunity to pull in more work from other CPUs.
*/
if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
if (likely((prev->sched_class == &idle_sched_class ||
prev->sched_class == &fair_sched_class) &&
rq->nr_running == rq->cfs.h_nr_running)) {
p = fair_sched_class.pick_next_task(rq, prev, rf);
if (unlikely(p == RETRY_TASK))
goto again;