Date: Thu, 12 Jun 2003 05:04:12 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: Chris Mason <mason@suse.com>,
       Marc-Christian Petersen <m.c.p@wolk-project.de>,
       Jens Axboe <axboe@suse.de>, Marcelo Tosatti <marcelo@conectiva.com.br>,
       Georg Nikodym <georgn@somanetworks.com>,
       lkml <linux-kernel@vger.kernel.org>,
       Matthias Mueller <matthias.mueller@rz.uni-karlsruhe.de>
Subject: Re: [PATCH] io stalls
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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
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