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    SubjectRe: clock drift in set_task_cpu()

    * Jack Daniel <wanders.thirst@gmail.com> wrote:

    > Hi Ingo,
    >
    > [...]
    >
    > Any chance that you will be pulling in this fix ?

    It's already upstream, as of v2.6.36-rc3. See the commit notification
    email below from Aug 19.

    Thanks,

    Ingo

    ----- Forwarded message from tip-bot for Peter Zijlstra <peterz@infradead.org> -----

    Date: Fri, 20 Aug 2010 14:16:14 GMT
    From: tip-bot for Peter Zijlstra <peterz@infradead.org>
    To: linux-tip-commits@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com,
    a.p.zijlstra@chello.nl, peterz@infradead.org, pjohn@mvista.com,
    wanders.thirst@gmail.com, tglx@linutronix.de, mingo@elte.hu
    Subject: [tip:sched/urgent] sched: Fix rq->clock synchronization when migrating tasks

    Commit-ID: 861d034ee814917a83bd5de4b26e3b8336ddeeb8
    Gitweb: http://git.kernel.org/tip/861d034ee814917a83bd5de4b26e3b8336ddeeb8
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Thu, 19 Aug 2010 13:31:43 +0200
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Fri, 20 Aug 2010 14:59:01 +0200

    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>
    ---
    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 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);

    ----- End forwarded message -----

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