Commit 1e78cdbd authored Feb 16, 2015 by Rik van Riel Committed by Ingo Molnar Feb 18, 2015

sched/rt/nohz: Stop scheduler tick if running realtime task



If the CPU is running a realtime task that does not round-robin
with another realtime task of equal priority, there is no point
in keeping the scheduler tick going. After all, whenever the
scheduler tick runs, the kernel will just decide not to
reschedule.

Extend sched_can_stop_tick() to recognize these situations, and
inform the rest of the kernel that the scheduler tick can be
stopped.

Tested-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: fweisbec@redhat.com
Cc: mtosatti@redhat.com
Link: http://lkml.kernel.org/r/20150216152349.6a8ed824@annuminas.surriel.com


[ Small cleanliness tweak. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 890a5409

kernel/sched/core.c

+17 −0

Original line number	Diff line number	Diff line
		@@ -689,6 +689,23 @@ static inline bool got_nohz_idle_kick(void)
		#ifdef CONFIG_NO_HZ_FULL
		bool sched_can_stop_tick(void)
		{
		/*
		* FIFO realtime policy runs the highest priority task. Other runnable
		* tasks are of a lower priority. The scheduler tick does nothing.
		*/
		if (current->policy == SCHED_FIFO)
		return true;

		/*
		* Round-robin realtime tasks time slice with other tasks at the same
		* realtime priority. Is this task the only one at this priority?
		*/
		if (current->policy == SCHED_RR) {
		struct sched_rt_entity *rt_se = &current->rt;

		return rt_se->run_list.prev == rt_se->run_list.next;
		}

		/*
		* More than one running task need preemption.
		* nr_running update is assumed to be visible

Admin message