From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753006Ab2GRILS (ORCPT ); Wed, 18 Jul 2012 04:11:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62516 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751275Ab2GRILJ (ORCPT ); Wed, 18 Jul 2012 04:11:09 -0400 Message-ID: <50067009.9030508@redhat.com> Date: Wed, 18 Jul 2012 16:12:57 +0800 From: Asias He User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 MIME-Version: 1.0 To: Stefan Hajnoczi CC: Paolo Bonzini , linux-kernel@vger.kernel.org, linux-aio@kvack.org, kvm@vger.kernel.org, "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, Benjamin LaHaise , Alexander Viro , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 0/5] Add vhost-blk support References: <1342107302-28116-1-git-send-email-asias@redhat.com> <50052276.2080906@redhat.com> <500527BA.9000001@redhat.com> <50052E7E.6020100@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/17/2012 07:11 PM, Stefan Hajnoczi wrote: > On Tue, Jul 17, 2012 at 10:21 AM, Asias He wrote: >> On 07/17/2012 04:52 PM, Paolo Bonzini wrote: >>> >>> Il 17/07/2012 10:29, Asias He ha scritto: >>>> >>>> So, vhost-blk at least saves ~6 syscalls for us in each request. >>> >>> >>> Are they really 6? If I/O is coalesced by a factor of 3, for example >>> (i.e. each exit processes 3 requests), it's really 2 syscalls per request. >> >> >> Well. I am counting the number of syscalls in one notify and response >> process. Sure the IO can be coalesced. > > Linux AIO also supports batching in io_submit() and io_getevents(). > Depending on the request pattern in the vring when you process it, you > should be able to do better than 1 set of syscalls per host I/O > request. > > Are you taking advantage of that at the moment in your userspace benchmark? OK. I know that batching in io_submit() and io_getevetns(). There was a patch for kvm tool long time ago. Now, both vhost-blk and kvm tool are not taking advantage of that atm. There are issues: e.g. How many number of request we want to batch? Does this batching hurt latency? -- Asias