[34-longterm 091/260] sched: Fix rq->clock synchronization when migrating tasks

Paul Gortmaker
2011-01-02T07:57:49Z

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: Paul Gortmaker <paul.gortmaker@windriver.com>
---
kernel/sched_fair.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 684e173..461d312 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3588,6 +3588,8 @@ 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);

--
1.7.3.3