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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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