lkml.org 
[lkml]   [2002]   [Jan]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: The O(1) scheduler breaks UML
On Sun, 13 Jan 2002, Jeff Dike wrote:

> The new scheduler holds IRQs off across the call to context_switch. UML's
> _switch_to expects them to be enabled when it is called, and things go
> badly wrong when they are not.
>
> Because UML has a host process for each UML thread, SIGIO needs to be
> forwarded from one process to the next during a context switch. A SIGIO
> arriving during the window between the disabling of IRQs and forwarding of
> IRQs to the next process will be trapped on the process going out of
> context. This happens fairly regularly and causes hangs because some process
> is waiting for disk IO which never arrives because the process that was notified
> of the completion is switched out.
>
> So, is it possible to enable IRQs across the call to _switch_to?

Yes, this should work :


if (likely(prev != next)) {
rq->nr_switches++;
rq->curr = next;
next->cpu = prev->cpu;
spin_unlock_irq(&rq->lock);
context_switch(prev, next);
} else
spin_unlock_irq(&rq->lock);
and there's no need for barrier() and rq reload in this way.




- Davide


-
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: 2005-03-22 13:15    [from the cache]
©2003-2011 Jasper Spaans