Messages in this thread Patch in this message | | | From | Gregory Haskins <> | Subject | [PATCH 2/3] sched: fix SCHED_FAIR wake-idle logic error | Date | Tue, 27 May 2008 18:59:39 -0600 |
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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> ---
kernel/sched_fair.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 24c0830..0ade6f8 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -951,7 +951,7 @@ 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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