From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752051Ab2FRLO6 (ORCPT ); Mon, 18 Jun 2012 07:14:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52562 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751660Ab2FRLO4 (ORCPT ); Mon, 18 Jun 2012 07:14:56 -0400 Message-ID: <4FDF0DA7.40604@redhat.com> Date: Mon, 18 Jun 2012 14:14:47 +0300 From: Dor Laor Reply-To: dlaor@redhat.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Rusty Russell CC: Asias He , 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 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> In-Reply-To: <87zk81x7dp.fsf@rustcorp.com.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18/2012 01:05 PM, Rusty Russell wrote: > On Mon, 18 Jun 2012 16:03:23 +0800, Asias He wrote: >> On 06/18/2012 03:46 PM, Rusty Russell wrote: >>> On Mon, 18 Jun 2012 14:53:10 +0800, Asias He wrote: >>>> This patch introduces bio-based IO path for virtio-blk. >>> >>> Why make it optional? >> >> request-based IO path is useful for users who do not want to bypass the >> IO scheduler in guest kernel, e.g. users using spinning disk. For users >> using fast disk device, e.g. SSD device, they can use bio-based IO path. > > Users using a spinning disk still get IO scheduling in the host though. > What benefit is there in doing it in the guest as well? The io scheduler waits for requests to merge and thus batch IOs together. It's not important w.r.t spinning disks since the host can do it but it causes much less vmexits which is the key issue for VMs. > > Cheers, > Rusty. > _______________________________________________ > Virtualization mailing list > Virtualization@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/virtualization From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dor Laor Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk Date: Mon, 18 Jun 2012 14:14:47 +0300 Message-ID: <4FDF0DA7.40604@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> Reply-To: dlaor@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig To: Rusty Russell Return-path: In-Reply-To: <87zk81x7dp.fsf@rustcorp.com.au> 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 List-Id: kvm.vger.kernel.org On 06/18/2012 01:05 PM, Rusty Russell wrote: > On Mon, 18 Jun 2012 16:03:23 +0800, Asias He wrote: >> On 06/18/2012 03:46 PM, Rusty Russell wrote: >>> On Mon, 18 Jun 2012 14:53:10 +0800, Asias He wrote: >>>> This patch introduces bio-based IO path for virtio-blk. >>> >>> Why make it optional? >> >> request-based IO path is useful for users who do not want to bypass the >> IO scheduler in guest kernel, e.g. users using spinning disk. For users >> using fast disk device, e.g. SSD device, they can use bio-based IO path. > > Users using a spinning disk still get IO scheduling in the host though. > What benefit is there in doing it in the guest as well? The io scheduler waits for requests to merge and thus batch IOs together. It's not important w.r.t spinning disks since the host can do it but it causes much less vmexits which is the key issue for VMs. > > Cheers, > Rusty. > _______________________________________________ > Virtualization mailing list > Virtualization@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/virtualization