From: Peter Zijlstra <peterz@infradead.org>

Date: Thu, 19 Aug 2010 11:31:43 +0000 (+0200)

Subject: sched: Fix rq->clock synchronization when migrating tasks

X-Git-Tag: v2.6.36-rc3~25^2~1

X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=861d034ee814917a83bd5de4b26e3b8336ddeeb8

sched: Fix rq->clock synchronization when migrating tasks

sched_fork() -- we do task placement in ->task_fork_fair() ensure we

  update_rq_clock() so we work with current time. We leave the vruntime

  in relative state, so the time delay until wake_up_new_task() doesn't

  matter.

wake_up_new_task() -- Since task_fork_fair() left p->vruntime in

  relative state we can safely migrate, the activate_task() on the

  remote rq will call update_rq_clock() and causes the clock to be

  synced (enough).

Tested-by: Jack Daniel <wanders.thirst@gmail.com>

Tested-by: Philby John <pjohn@mvista.com>

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

LKML-Reference: <1281002322.1923.1708.camel@laptop>

Signed-off-by: Ingo Molnar <mingo@elte.hu>

---

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c

index 09a9811..6cebdf8 100644

--- a/kernel/sched_fair.c

+++ b/kernel/sched_fair.c

@@ -3609,6 +3609,8 @@ static void task_fork_fair(struct task_struct *p)

 	raw_spin_lock_irqsave(&rq->lock, flags);

+	update_rq_clock(rq);

+

 	if (unlikely(task_cpu(p) != this_cpu)) {

 		rcu_read_lock();

 		__set_task_cpu(p, this_cpu);