Re: [PATCH 18/45] writeback: introduce wait queue forbalance_dirty_pages()

[Jens Axboe]

On Thu, Oct 08 2009, Peter Zijlstra wrote:
> On Thu, 2009-10-08 at 09:58 +0800, Wu Fengguang wrote:
> > 
> > > How this runqueue->nr_iowait is handled now ?
> > 
> > Good question. io_schedule() has an old comment for throttling IO wait:
> > 
> >          * But don't do that if it is a deliberate, throttling IO wait (this task
> >          * has set its backing_dev_info: the queue against which it should throttle)
> >          */
> >         void __sched io_schedule(void)
> > 
> > So it looks both Jens' and this patch behaves right in ignoring the
> > iowait accounting for balance_dirty_pages() :)
> 
> Well it is a change in behaviour, and I think IOWAIT makes sense when
> we're blocked due to io throttle..
> 
> Hmm?

Yep agree, if we're deliberately waiting on IO, it should count as
iowait time.

-- 
Jens Axboe

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