Commit 0ba87bb2 authored Mar 01, 2017 by Peter Zijlstra Committed by Ingo Molnar Mar 02, 2017

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



Pavan noticed that the following commit:

  49ee5768 ("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: 49ee5768 ("sched/core: Optimize pick_next_task() for idle_sched_class")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4c77b18c

kernel/sched/core.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -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;