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From: Peter Zijlstra <>
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

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

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 <>
Tested-by: Philby John <>
Signed-off-by: Peter Zijlstra <>
LKML-Reference: <1281002322.1923.1708.camel@laptop>
Signed-off-by: Ingo Molnar <>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 806d1b2..ab661eb 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3752,6 +3752,8 @@ 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))
 		__set_task_cpu(p, this_cpu);