From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=48097 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OEfEs-0002gc-6f for qemu-devel@nongnu.org; Wed, 19 May 2010 05:06:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OEfEo-0000Dl-H0 for qemu-devel@nongnu.org; Wed, 19 May 2010 05:06:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45244) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OEfEo-0000DV-9l for qemu-devel@nongnu.org; Wed, 19 May 2010 05:06:50 -0400 Message-ID: <4BF3AA1E.4050307@redhat.com> Date: Wed, 19 May 2010 12:06:38 +0300 From: Avi Kivity MIME-Version: 1.0 References: <1274203124-14318-1-git-send-email-avi@redhat.com> <4BF39CA3.9020305@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH +stable] block: don't attempt to merge overlapping requests List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , qemu-devel@nongnu.org, kvm@vger.kernel.org, Christoph Hellwig On 05/19/2010 12:01 PM, Stefan Hajnoczi wrote: > On Wed, May 19, 2010 at 9:09 AM, Avi Kivity wrote: > >> On 05/18/2010 10:22 PM, Stefan Hajnoczi wrote: >> >>> What cache= mode are you running? >>> >> writeback. >> > In the cache=writeback case the virtio-blk guest driver does: > > blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH, ...) > I don't follow. What's the implication? btw I really dislike how the cache attribute (which I see as a pure host choice) is exposed to the guest. It means we can't change caching mode on the fly (for example after live migration), or that changing caching mode during a restart may expose a previously hidden guest bug. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.