From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752997Ab2GTU4Y (ORCPT ); Fri, 20 Jul 2012 16:56:24 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:42128 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750939Ab2GTU4X (ORCPT ); Fri, 20 Jul 2012 16:56:23 -0400 From: Anthony Liguori To: "Michael S. Tsirkin" Cc: Asias He , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support In-Reply-To: <20120719130957.GD9303@redhat.com> References: <1342169711-12386-1-git-send-email-asias@redhat.com> <1342169711-12386-6-git-send-email-asias@redhat.com> <87mx2vrjdl.fsf@codemonkey.ws> <20120719130957.GD9303@redhat.com> User-Agent: Notmuch/0.13.2+60~g7ecf77d (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) Date: Fri, 20 Jul 2012 15:56:19 -0500 Message-ID: <87obnaup70.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Michael S. Tsirkin" writes: > On Thu, Jul 19, 2012 at 08:05:42AM -0500, Anthony Liguori wrote: >> Of course, the million dollar question is why would using AIO in the >> kernel be faster than using AIO in userspace? > > Actually for me a more important question is how does it compare > with virtio-blk dataplane? I'm not even asking for a benchmark comparision. It's the same API being called from a kernel thread vs. a userspace thread. Why would there be a 60% performance difference between the two? That doesn't make any sense. There's got to be a better justification for putting this in the kernel than just that we can. I completely understand why Christoph's suggestion of submitting BIOs directly would be faster. There's no way to do that in userspace. Regards, Anthony Liguori > > -- > MST