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    SubjectRe: [RFC][PATCH 2/3] sched, workqueue: Move WQ-sleeper wakeup
    Hello, Peter.

    On Wed, Jun 22, 2011 at 01:34:46AM +0200, Peter Zijlstra wrote:
    > -/**
    > * wake_up_process - Wake up a specific process
    > * @p: The process to be woken up.
    > *
    > @@ -4215,6 +4181,19 @@ static inline void sched_submit_work(voi
    >
    > if (tsk->state && !(preempt_count() & PREEMPT_ACTIVE)) {
    > /*
    > + * If a worker went to sleep, notify and ask workqueue
    > + * whether it wants to wake up a task to maintain
    > + * concurrency.
    > + */
    > + if (tsk->flags & PF_WQ_WORKER) {
    > + struct task_struct *to_wakeup;
    > +
    > + to_wakeup = wq_worker_sleeping(tsk, smp_processor_id());
    > + if (to_wakeup)
    > + wake_up_process(to_wakeup);
    > + }
    > +
    > + /*

    Preemption could still be enabled here, right? What prevents
    preemtion kicking after wq_worker_sleeping() and do it again thus
    breaking nr_running tracking.

    > * If we are going to sleep and we have plugged IO
    > * queued, make sure to submit it to avoid deadlocks.
    > */
    > @@ -4256,19 +4235,6 @@ asmlinkage void __sched schedule(void)
    > } else {
    > deactivate_task(rq, prev, DEQUEUE_SLEEP);
    > prev->on_rq = 0;
    > -
    > - /*
    > - * If a worker went to sleep, notify and ask workqueue
    > - * whether it wants to wake up a task to maintain
    > - * concurrency.
    > - */
    > - if (prev->flags & PF_WQ_WORKER) {
    > - struct task_struct *to_wakeup;
    > -
    > - to_wakeup = wq_worker_sleeping(prev, cpu);
    > - if (to_wakeup)
    > - try_to_wake_up_local(to_wakeup);
    > - }

    Similarly, the if the 'if {}' part of the above if/else is taken, the
    task never goes to sleep and nr_running will again be broken.

    --
    tejun


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