Messages in this thread | | | Date | Wed, 21 Aug 2013 10:31:30 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock |
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On Tue, Aug 20, 2013 at 08:25:53PM +0200, Oleg Nesterov wrote: > On 08/20, Peter Zijlstra wrote: > > > > On Tue, Aug 20, 2013 at 06:33:12PM +0200, Oleg Nesterov wrote:
> > > + if (unlikely(prev->in_iowait)) { > > > + raw_spin_lock_irq(&rq->lock); > > > + rq->nr_iowait--; > > > + raw_spin_unlock_irq(&rq->lock); > > > + } > > > > This seems like the wrong place, this is where you return from > > schedule() running another task, > > Yes, but prev is current, and rq should be "correct" for > rq->nr_iowait-- ?
Yes its the right rq, but the wrong time.
> This local var should be equal to its value when this task called > context_switch() in the past. > > Like any other variable, like "rq = raw_rq()" in io_schedule(). > > > not where the task you just send to > > sleep wakes up. > > sure, but currently io_schedule() does the same.
No it doesn't. It only does the decrement when the task is woken back up. Not right after it switches out.
> Btw. Whatever we do, can't we unify io_schedule/io_schedule_timeout?
I suppose we could, a timeout of MAX_SCHEDULE_TIMEOUT will act like a regular schedule, but it gets all the overhead of doing schedule_timeout(). So I don't think its a win.
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