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Subject[102/123] sched: Fix rq->clock synchronization when migrating tasks
From: Peter Zijlstra <peterz@infradead.org>

commit 861d034ee814917a83bd5de4b26e3b8336ddeeb8 upstream

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>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
kernel/sched_fair.c | 2 ++
1 file changed, 2 insertions(+)

--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1963,6 +1963,8 @@ static void task_fork_fair(struct task_s

spin_lock_irqsave(&rq->lock, flags);

+ update_rq_clock(rq);
+
if (unlikely(task_cpu(p) != this_cpu))
__set_task_cpu(p, this_cpu);




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