From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51048) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sm3UL-0001sg-Ug for qemu-devel@nongnu.org; Tue, 03 Jul 2012 09:50:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Sm3UH-0003Vr-4I for qemu-devel@nongnu.org; Tue, 03 Jul 2012 09:49:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46124) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sm3UG-0003VM-SS for qemu-devel@nongnu.org; Tue, 03 Jul 2012 09:49:53 -0400 Message-ID: <4FF2F87C.6010600@redhat.com> Date: Tue, 03 Jul 2012 15:49:48 +0200 From: Kevin Wolf MIME-Version: 1.0 References: <1341321642-24598-1-git-send-email-pbonzini@redhat.com> <1341321642-24598-3-git-send-email-pbonzini@redhat.com> In-Reply-To: <1341321642-24598-3-git-send-email-pbonzini@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 2/2] virtio-blk: disable write cache if not negotiated List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: anthony@codemonkey.ws, rusty@rustcorp.com.au, qemu-devel@nongnu.org, kvm@vger.kernel.org, mst@redhat.com Am 03.07.2012 15:20, schrieb Paolo Bonzini: > If the guest does not support flushes, we should run in writethrough mode. > The setting is temporary until the next reset, so that for example the > BIOS will run in writethrough mode while Linux will run with a writeback > cache. > > VIRTIO_BLK_F_FLUSH has been introduced in Linux 2.6.32 (in 2009) and > was backported to RHEL/CentOS 5.6 (in 2010). The Windows drivers have > two bugs, which I reported on the Red Hat Bugzilla as bugs 837321 and > 837324. With these patches they will suffer a performance hit but > gain correctness. > > Signed-off-by: Paolo Bonzini I generally like the idea for a default, but doesn't this override even an explicit cache=writeback? Are we sure that we want this? Kevin