Re: [PATCH] io stalls

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Jun 12, 2003 at 12:51:30PM +1000, Nick Piggin wrote:
> I guess you could fix this by having a "last woken" flag, and
> allow that process to allocate requests without blocking from
> the batch limit until the queue full limit. That is how
> batch_requests is supposed to work.

I see what you mean, I did care about the case of each request belonging
to a different task, but of course this doesn't work if there's just one
task. In such case there will be a single wakeup and one for each
request, so it won't be able to eat all the requests and it'll keep
hanging on the full bitflag. So yes, the ->full bit partly disabled the
batch sectors in presence of only 1 task. With multiple tasks and the
wake_up_nr batch_sectors will still work. However I don't care about
that right now ;), it's a minor issue I guess, single task I/O normally
doesn't seek heavily so more likely it will run into the oversized queue
before being able to take advantage of the batch sectors.

Andrea