lkml.org 
[lkml]   [2010]   [May]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCHv4 17/17] writeback: lessen sync_supers wakeup count
From
Date
On Mon, 2010-05-31 at 22:47 +1000, Nick Piggin wrote:
> > set_current_state(TASK_INTERRUPTIBLE);
> > /*
> > * XXX: what if we are preempted here. No timer is armed. Our state is
> > * TASK_INTERRUPTIBLE, supers_dirty is 1, so no one will ever wake us
> > * up. Thus, we'll sleep forever.
> > */
> > if (supers_dirty)
> > bdi_arm_supers_timer();
> > schedule();
> >
> > Not sure, but I did quick search and it looks like in preemptive kernel,
> > an interrupt may happen in the XXX place above, then it will call
> > 'preempt_schedule_irq()', which sill call 'schedule()'.
>
> Yes, preempt does not participate in tsak sleeping exactly for reasons
> such as this.
>
> From kernel/sched.c:schedule()
>
> if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
> if (unlikely(signal_pending_state(prev->state, prev)))
> prev->state = TASK_RUNNING;
> else
> deactivate_task(rq, prev, DEQUEUE_SLEEP);
> switch_count = &prev->nvcsw;
> }
>
> If the task is not running, then is only removed from the runqueue
> (or reset to running in case of pending signal) IFF it has not been
> scheduled from an involuntary kernel preemption.
>
> So in the XXX region, the task will actually be allowed to run again
> until it calls schedule().

Clear now, thanks a lot again!

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2010-05-31 15:07    [W:0.930 / U:0.460 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site