Commit 104f6454 authored Apr 28, 2008 by Gregory Haskins Committed by Ingo Molnar May 05, 2008

sched: fix SCHED_FAIR wake-idle logic error



We currently use an optimization to skip the overhead of wake-idle
processing if more than one task is assigned to a run-queue.  The
assumption is that the system must already be load-balanced or we
wouldnt be overloaded to begin with.

The problem is that we are looking at rq->nr_running, which may include
RT tasks in addition to CFS tasks.  Since the presence of RT tasks
really has no bearing on the balance status of CFS tasks, this throws
the calculation off.

This patch changes the logic to only consider the number of CFS tasks
when making the decision to optimze the wake-idle.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 8ae121ac

kernel/sched_fair.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1009,7 +1009,7 @@ static int wake_idle(int cpu, struct task_struct *p)
		* sibling runqueue info. This will avoid the checks and cache miss
		* penalities associated with that.
		*/
		if (idle_cpu(cpu) \|\| cpu_rq(cpu)->nr_running > 1)
		if (idle_cpu(cpu) \|\| cpu_rq(cpu)->cfs.nr_running > 1)
		return cpu;

		for_each_domain(cpu, sd) {

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