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    SubjectRe: [Question] sched: Should nr_uninterruptible be decremented in ttwu_do_activate()?
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    On Thu, 2012-01-12 at 12:09 +0600, Rakib Mullick wrote:
    > On Wed, Jan 11, 2012 at 11:29 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    > > On Wed, 2012-01-11 at 23:22 +0600, Rakib Mullick wrote:
    > >> Hello all,
    > >>
    > >> In ttwu_do_activate(), we're decrementing nr_uninterruptible if
    > >> p->sched_contributes_to_load (for SMP=y). But, we're also decrementing
    > >> nr_uninterruptible from activate_task at the same path. Why we're
    > >> doing it twice for a single task activation path?
    > >
    > > activate_task() does:
    > >
    > > if (task_contributes_to_load(p))
    > > rq->nr_uninterruptible--;
    > >
    > > Now task_contributes_to_load() reads like:
    > >
    > > #define task_contributes_to_load(task) \
    > > ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
    > > (task->flags & PF_FREEZING) == 0)
    > >
    > > which will be false, since we've set TASK_WAKING.
    >
    > Enough confusing. TASK_WAKING will be set when called from
    > try_to_wake_up(). ttwu_do_activate() gets called from other places:
    > scheduler_ipi() and sched_ttwu_pending() (at the time of cpu goes
    > down). TASK_WAKING will be not set at that time,

    Yes it will be, the only way to get on that list is throught
    ttwu_queue_remote() at which point tasks are TASK_WAKING.

    > moreover it is
    > possible that, task has p->sched_contributes_to_load is set and latter
    > on gets wake up by sched_ttwu_pending/scheduler_ipi() call.

    That's the entire point. But all ways to ttwu_queue_remote() explicitly
    set ->sched_contributes_to_load.


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