From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk Date: Wed, 04 Jul 2012 12:10:42 +0930 Message-ID: <87lij0w8np.fsf@rustcorp.com.au> References: <1340002390-3950-1-git-send-email-asias@redhat.com> <1340002390-3950-4-git-send-email-asias@redhat.com> <87hau9yse7.fsf@rustcorp.com.au> <4FDEE0CB.1030505@redhat.com> <87zk81x7dp.fsf@rustcorp.com.au> <4FDF0DA7.40604@redhat.com> <1340019575.22848.2.camel@lappy> <4FDFE926.7030309@redhat.com> <87r4svxcjw.fsf@rustcorp.com.au> <4FF10B31.60609@redhat.com> <8762a6y89v.fsf@rustcorp.com.au> <4FF23F4B.2040803@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FF23F4B.2040803@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Asias He Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Sasha Levin , Christoph Hellwig List-Id: virtualization@lists.linuxfoundation.org On Tue, 03 Jul 2012 08:39:39 +0800, Asias He wrote: > On 07/02/2012 02:41 PM, Rusty Russell wrote: > > Sure, our guest merging might save us 100x as many exits as no merging. > > But since we're not doing many requests, does it matter? > > We can still have many requests with slow devices. The number of > requests depends on the workload in guest. E.g. 512 IO threads in guest > keeping doing IO. You can have many requests outstanding. But if the device is slow, the rate of requests being serviced must be low. Am I misunderstanding something? I thought if you could have a high rate of requests, it's not a slow device. Cheers, Rusty. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751341Ab2GDEHN (ORCPT ); Wed, 4 Jul 2012 00:07:13 -0400 Received: from ozlabs.org ([203.10.76.45]:47398 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750841Ab2GDEHJ (ORCPT ); Wed, 4 Jul 2012 00:07:09 -0400 From: Rusty Russell To: Asias He Cc: Sasha Levin , dlaor@redhat.com, kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk In-Reply-To: <4FF23F4B.2040803@redhat.com> References: <1340002390-3950-1-git-send-email-asias@redhat.com> <1340002390-3950-4-git-send-email-asias@redhat.com> <87hau9yse7.fsf@rustcorp.com.au> <4FDEE0CB.1030505@redhat.com> <87zk81x7dp.fsf@rustcorp.com.au> <4FDF0DA7.40604@redhat.com> <1340019575.22848.2.camel@lappy> <4FDFE926.7030309@redhat.com> <87r4svxcjw.fsf@rustcorp.com.au> <4FF10B31.60609@redhat.com> <8762a6y89v.fsf@rustcorp.com.au> <4FF23F4B.2040803@redhat.com> User-Agent: Notmuch/0.12 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Wed, 04 Jul 2012 12:10:42 +0930 Message-ID: <87lij0w8np.fsf@rustcorp.com.au> 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 On Tue, 03 Jul 2012 08:39:39 +0800, Asias He wrote: > On 07/02/2012 02:41 PM, Rusty Russell wrote: > > Sure, our guest merging might save us 100x as many exits as no merging. > > But since we're not doing many requests, does it matter? > > We can still have many requests with slow devices. The number of > requests depends on the workload in guest. E.g. 512 IO threads in guest > keeping doing IO. You can have many requests outstanding. But if the device is slow, the rate of requests being serviced must be low. Am I misunderstanding something? I thought if you could have a high rate of requests, it's not a slow device. Cheers, Rusty.