From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754437Ab2G3Nvn (ORCPT ); Mon, 30 Jul 2012 09:51:43 -0400 Received: from verein.lst.de ([213.95.11.211]:49782 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754305Ab2G3NvQ (ORCPT ); Mon, 30 Jul 2012 09:51:16 -0400 X-Greylist: delayed 507 seconds by postgrey-1.27 at vger.kernel.org; Mon, 30 Jul 2012 09:51:16 EDT Date: Mon, 30 Jul 2012 15:42:47 +0200 From: Christoph Hellwig To: Rusty Russell Cc: "Michael S. Tsirkin" , Asias He , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, Christoph Hellwig , Minchan Kim Subject: Re: [PATCH V4 3/3] virtio-blk: Add bio-based IO path for virtio-blk Message-ID: <20120730134247.GA6041@lst.de> References: <1343442065-15646-1-git-send-email-asias@redhat.com> <1343442065-15646-4-git-send-email-asias@redhat.com> <20120729111115.GD8977@redhat.com> <87a9yim2qg.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a9yim2qg.fsf@rustcorp.com.au> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 30, 2012 at 11:25:51AM +0930, Rusty Russell wrote: > I consider this approach a half-way step. Quick attempts on my laptop > and I couldn't find a case where the bio path was a loss, but in theory > if the host wasn't doing any reordering and it was a slow device, you'd > want the guest to do so. > > I'm not sure if current qemu can be configured to do such a thing? The host kernel will do the I/O scheduling for you unless you explicitly disable it. And we should be able to assume an administrator will only disable it when they have a reason for it - if not they'll get worse performance for non-virtualized workloads as well.