Re: [PATCH] io stalls

[Andrea Arcangeli]

On Thu, Jun 12, 2003 at 12:41:58PM +1000, Nick Piggin wrote:
> 
> 
> Chris Mason wrote:
> 
> >On Wed, 2003-06-11 at 21:29, Andrea Arcangeli wrote:
> >
> >
> >>this will avoid get_request_wait_wakeup to mess the wakeup, so we can
> >>wakep_nr(rq.count) safely.
> >>
> >>then there's the last issue raised by Chris, that is if we get request
> >>released faster than the tasks can run, still we can generate a not
> >>perfect fairness. My solution to that is to change wake_up to have a
> >>nr_exclusive not obeying to the try_to_wakeup retval. that should
> >>guarantee exact FIFO then, but it's a minor issue because the requests
> >>shouldn't be released systematically in a flood. So I'm leaving it
> >>opened for now, the others already addressed should be the major ones.
> >>
> >
> >I think the only time we really need to wakeup more than one waiter is
> >when we hit the q->batch_request mark.  After that, each new request
> >that is freed can be matched with a single waiter, and we know that any
> >previously finished requests have probably already been matched to their
> >own waiter.
> >
> >
> Nope. Not even then. Each retiring request should submit
> a wake up, and the process will submit another request.
> So the number of requests will be held at the batch_request
> mark until no more waiters.
> 
> Now that begs the question, why have batch_requests anymore?
> It no longer does anything.

it does nothing w/ _exclusive and w/o the wake_up_nr, that's why I added
the wake_up_nr.

Andrea