From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCH 11/20] nbd: request_fn fixup Date: Tue, 12 Sep 2006 20:21:06 -0400 Message-ID: <45074EF2.3080407@garzik.org> References: <20060912143049.278065000@chello.nl> <20060912144904.197253000@chello.nl> <20060912224710.GB23515@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Linus Torvalds , Andrew Morton , David Miller , Rik van Riel , Daniel Phillips , Pavel Machek Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:29826 "EHLO mail.dvmed.net") by vger.kernel.org with ESMTP id S1030428AbWIMAVT (ORCPT ); Tue, 12 Sep 2006 20:21:19 -0400 To: Jens Axboe In-Reply-To: <20060912224710.GB23515@kernel.dk> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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