Commit 1f3b0f82 authored Jul 14, 2016 by Gaurav Jindal Committed by Thomas Gleixner Jul 19, 2016

tick/nohz: Optimize nohz idle enter



tick_nohz_start_idle is called before checking whether the idle tick can be
stopped. If the tick cannot be stopped, calling tick_nohz_start_idle() is
pointless and just wasting CPU cycles.

Only invoke tick_nohz_start_idle() when can_stop_idle_tick() returns true. A
short one minute observation of the effect on ARM64 shows a reduction of calls
by 1.5% thus optimizing the idle entry sequence.

[tglx: Massaged changelog ]

Co-developed-by: Sanjeev <Yadav&lt;sanjeev.yadav@spreadtrum.com>
Signed-off-by: Gaurav <Jindal&lt;gaurav.jindal@spreadtrum.com>
Link: http://lkml.kernel.org/r/20160714120416.GB21099@gaurav.jindal@spreadtrum.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent 775be506

kernel/time/tick-sched.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -908,11 +908,10 @@ static void __tick_nohz_idle_enter(struct tick_sched *ts)
		ktime_t now, expires;
		int cpu = smp_processor_id();

		now = tick_nohz_start_idle(ts);

		if (can_stop_idle_tick(cpu, ts)) {
		int was_stopped = ts->tick_stopped;

		now = tick_nohz_start_idle(ts);
		ts->idle_calls++;

		expires = tick_nohz_stop_sched_tick(ts, now, cpu);