linux-kernel - Re: [PATCH 11/20] nbd: request

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Date:	Tue, 12 Sep 2006 20:21:06 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Jens Axboe <axboe@...nel.dk>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	David Miller <davem@...emloft.net>,
	Rik van Riel <riel@...hat.com>,
	Daniel Phillips <phillips@...gle.com>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 11/20] nbd: request_fn fixup

Jens Axboe wrote:
> Generally the block device rule is that once you are invoked due to an
> unplug (or whatever) event, it is the responsibility of the block device
> to run the queue until it's done. So if you bail out of queue handling
> for whatever reason (might be resource starvation in hard- or software),
> you must make sure to reenter queue handling since the device will not
> get replugged while it has requests pending. Unless you run into some
> software resource shortage, running of the queue is done
> deterministically when you know resources are available (ie an io
> completes). The device plugging itself is only ever done when you
> encounter a shortage outside of your control (memory shortage, for
> instance) _and_ you don't already have pending work where you can invoke
> queueing from again.

Or he could employ the blk_{start,stop}_queue() functions, if that model 
is easier for the driver (and brain).

	Jeff


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