From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [QEMU PATCH 0/2] virtio-blk: writeback cache enable improvements Date: Mon, 23 Jul 2012 18:32:38 +0200 Message-ID: <500D7CA6.5090901@redhat.com> References: <1341321642-24598-1-git-send-email-pbonzini@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, kwolf@redhat.com, rusty@rustcorp.com.au To: unlisted-recipients:; (no To-header on input) Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:53648 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753616Ab2GWQcx (ORCPT ); Mon, 23 Jul 2012 12:32:53 -0400 Received: by pbbrp8 with SMTP id rp8so11115062pbb.19 for ; Mon, 23 Jul 2012 09:32:52 -0700 (PDT) In-Reply-To: <1341321642-24598-1-git-send-email-pbonzini@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 03/07/2012 15:20, Paolo Bonzini ha scritto: > These patches let virtio-blk use the new support for toggling the cache > mode between writethrough and writeback. > > The first patch introduces a new feature bit and configuration field to > do this. The second patch disables writeback caching for guests that do > not negotiate VIRTIO_BLK_F_WCACHE (meaning that they cannot send flush > requests), so that limited or older guests are now safe wrt power losses. > 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 (which work by emulating SCSI on top of virtio-blk) > have bugs in this area, 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. > > Paolo Bonzini (2): > virtio-blk: support VIRTIO_BLK_F_CONFIG_WCE > virtio-blk: disable write cache if not negotiated Ping - Anthony, mst? Paolo