Commit ff6f2d29 authored Jan 21, 2015 by Preeti U Murthy Committed by Ingo Molnar Jan 30, 2015

sched/idle: Add missing checks to the exit condition of cpu_idle_poll()



cpu_idle_poll() is entered into when either the cpu_idle_force_poll is set or
tick_check_broadcast_expired() returns true. The exit condition from
cpu_idle_poll() is tif_need_resched().

However this does not take into account scenarios where cpu_idle_force_poll
changes or tick_check_broadcast_expired() returns false, without setting
the resched flag. So a cpu will be caught in cpu_idle_poll() needlessly,
thereby wasting power. Add an explicit check on cpu_idle_force_poll and
tick_check_broadcast_expired() to the exit condition of cpu_idle_poll()
to avoid this.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20150121105655.15279.59626.stgit@preeti.in.ibm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent a18b5d01

kernel/sched/idle.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void)
		rcu_idle_enter();
		trace_cpu_idle_rcuidle(0, smp_processor_id());
		local_irq_enable();
		while (!tif_need_resched())
		while (!tif_need_resched() &&
		(cpu_idle_force_poll \|\| tick_check_broadcast_expired()))
		cpu_relax();
		trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
		rcu_idle_exit();

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