[patch] sched: add the other missing clock update to migra..

sched: add the other missing clock update to migrate_task()

When calling set_task_cpu(), we must update both runqueue clocks in order
to get an accurate clock offset. Add it.


Signed-off-by: Mike Galbraith <efault.DeleteThis@gmx.de>
Cc: Ingo Molnar <mingo.DeleteThis@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra.DeleteThis@chello.nl>
LKML-Reference: <new-submission>

---
kernel/sched.c | 1 +
1 file changed, 1 insertion(+)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2126,6 +2126,7 @@ migrate_task(struct task_struct *p, int
*/
if (!p->se.on_rq && !task_running(rq, p)) {
update_rq_clock(rq);
+ update_rq_clock(cpu_rq(dest_cpu));
set_task_cpu(p, dest_cpu);
return 0;
}


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On Sun, 2009-11-22 at 13:11 +0100, Mike Galbraith wrote:
> sched: add the other missing clock update to migrate_task()
>
> When calling set_task_cpu(), we must update both runqueue clocks in order
> to get an accurate clock offset. Add it.
>
>
> Signed-off-by: Mike Galbraith <efault.TakeThisOut@gmx.de>
> Cc: Ingo Molnar <mingo.TakeThisOut@elte.hu>
> Cc: Peter Zijlstra <a.p.zijlstra.TakeThisOut@chello.nl>
> LKML-Reference: <new-submission>
>
> ---
> kernel/sched.c | 1 +
> 1 file changed, 1 insertion(+)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -2126,6 +2126,7 @@ migrate_task(struct task_struct *p, int
> */
> if (!p->se.on_rq && !task_running(rq, p)) {
> update_rq_clock(rq);
> + update_rq_clock(cpu_rq(dest_cpu));
> set_task_cpu(p, dest_cpu);
> return 0;
> }


We should make double_rq_lock() and double_lock_balance() behave
equivalent wrt update_rq_clock().

Current, depending on CONFIG_PREEMPT, double_lock_balance() already
updates both rq clocks.

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