From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 2/2] virtio-blk: disable write cache if not negotiated Date: Tue, 03 Jul 2012 15:51:27 +0200 Message-ID: <4FF2F8DF.4020806@redhat.com> References: <1341321642-24598-1-git-send-email-pbonzini@redhat.com> <1341321642-24598-3-git-send-email-pbonzini@redhat.com> <4FF2F87C.6010600@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, mst@redhat.com, anthony@codemonkey.ws, rusty@rustcorp.com.au To: Kevin Wolf Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60352 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750731Ab2GCNvj (ORCPT ); Tue, 3 Jul 2012 09:51:39 -0400 In-Reply-To: <4FF2F87C.6010600@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 03/07/2012 15:49, Kevin Wolf ha scritto: >> 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? Yes. It doesn't override cache=unsafe though. > Are we sure that we want this? The idea is that this change will overcome Anthony's objections to switching the default to writeback... Paolo