The following commit has been merged in the linux branch: commit f5dc37530ba8a35aae0f7f4f13781d1904f71e94 Author: Mike Galbraith efault@gmx.de Date: Fri Oct 9 08:35:03 2009 +0200

sched: Update the clock of runqueue select_task_rq() selected

In try_to_wake_up(), we update the runqueue clock, but select_task_rq() may select a different runqueue than the one we updated, leaving the new runqueue's clock stale for a bit.

This patch cures occasional huge latencies reported by latencytop when coming out of idle on a mostly idle NO_HZ box.

Signed-off-by: Mike Galbraith efault@gmx.de Signed-off-by: Peter Zijlstra a.p.zijlstra@chello.nl LKML-Reference: 1255070103.7639.30.camel@marge.simson.net Signed-off-by: Ingo Molnar mingo@elte.hu

diff --git a/kernel/sched.c b/kernel/sched.c index 76c0e96..e3f8f4f 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2311,7 +2311,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, { int cpu, orig_cpu, this_cpu, success = 0; unsigned long flags; - struct rq *rq; + struct rq *rq, *orig_rq;

if (!sched_feat(SYNC_WAKEUPS)) wake_flags &= ~WF_SYNC; @@ -2319,7 +2319,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, this_cpu = get_cpu();

smp_wmb(); - rq = task_rq_lock(p, &flags); + rq = orig_rq = task_rq_lock(p, &flags); update_rq_clock(rq); if (!(p->state & state)) goto out; @@ -2350,6 +2350,10 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, set_task_cpu(p, cpu);

rq = task_rq_lock(p, &flags); + + if (rq != orig_rq) + update_rq_clock(rq); + WARN_ON(p->state != TASK_WAKING); cpu = task_cpu(p);