From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH +stable] block: don't attempt to merge overlapping requests Date: Wed, 19 May 2010 12:06:38 +0300 Message-ID: <4BF3AA1E.4050307@redhat.com> References: <1274203124-14318-1-git-send-email-avi@redhat.com> <4BF39CA3.9020305@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Kevin Wolf , qemu-devel@nongnu.org, kvm@vger.kernel.org, Christoph Hellwig To: Stefan Hajnoczi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:29467 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756931Ab0ESJGu (ORCPT ); Wed, 19 May 2010 05:06:50 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: 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.