On Sun, 2007-05-06 at 16:47 +0400, Oleg Nesterov wrote:
> On 05/05, Tom Zanussi wrote:
> >
> > This patch makes relay use timers instead of workqueues for reader
> > waking.
>
> A couple of very minor nits,
>
> > @@ -337,11 +334,11 @@ static void __relay_reset(struct rchan_buf *buf,
> > unsigned int init)
> > if (init) {
> > init_waitqueue_head(&buf->read_wait);
> > kref_init(&buf->kref);
> > - INIT_DELAYED_WORK(&buf->wake_readers, NULL);
> > - } else {
> > - cancel_delayed_work(&buf->wake_readers);
> > - flush_scheduled_work();
> > - }
> > + init_timer(&buf->timer);
> > + buf->timer.data = (unsigned long)buf;
> > + buf->timer.function = wakeup_readers;
>
> I'd suggest to use setup_timer(&buf->timer, wakeup_readers, buf);
>
> > @@ -609,9 +605,16 @@ size_t relay_switch_subbuf(struct rchan_buf *buf,
> > size_t length)
> > buf->padding[old_subbuf];
> > smp_mb();
> > if (waitqueue_active(&buf->read_wait)) {
> > - PREPARE_DELAYED_WORK(&buf->wake_readers,
> > - wakeup_readers);
> > - schedule_delayed_work(&buf->wake_readers, 1);
> > + /*
> > + * Calling wake_up_interruptible() from here
> > + * will deadlock if we happen to be logging
> > + * from the scheduler (trying to re-grab
> > + * rq->lock), so defer it.
> > + */
> > + if (!timer_pending(&buf->timer)) {
> > + buf->timer.expires = jiffies + 1;
> > + add_timer(&buf->timer);
> > + }
>
> I think it is better to use __mod_timer(&buf->timer, jiffies + 1). In that
> case this "if (!timer_pending(&buf->timer))" is not strictly needed, yes?
>
> Imho, add_timer() is almost never should be used. The only valid usage is when
> timer->expires was already set by somebody else.
>
> Btw, thanks for your explanation about deferred wakeup.
>
OK, and thanks for your helpful comments. Corrected patch to follow...
Tom
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