From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=34231 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OEeLB-00085a-CQ for qemu-devel@nongnu.org; Wed, 19 May 2010 04:09:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OEeL4-0007eM-U1 for qemu-devel@nongnu.org; Wed, 19 May 2010 04:09:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52212) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OEeL3-0007e6-Uf for qemu-devel@nongnu.org; Wed, 19 May 2010 04:09:14 -0400 Message-ID: <4BF39CA3.9020305@redhat.com> Date: Wed, 19 May 2010 11:09:07 +0300 From: Avi Kivity MIME-Version: 1.0 References: <1274203124-14318-1-git-send-email-avi@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 05/18/2010 10:22 PM, Stefan Hajnoczi wrote: > On Tue, May 18, 2010 at 6:18 PM, Avi Kivity wrote: > >> The block multiwrite code pretends to be able to merge overlapping requests, >> but doesn't do so in fact. This leads to I/O errors (for example on mkfs >> of a large virtio disk). >> > Are overlapping write requests correct guest behavior? I thought the > ordering semantics require a flush between overlapping writes to > ensure A is written before B. > > What cache= mode are you running? > writeback. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.