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sched: Update the clock of runqueue select_task_rq() selected

Browse source 
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>
This commit is contained in:
Mike Galbraith 2009-10-09 08:35:03 +02:00 committed by Ingo Molnar
parent 36a07902c2
commit f5dc37530b
1 changed files with 6 additions and 2 deletions
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8
kernel/sched.c
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@ -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);