From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 0/5] Add vhost-blk support Date: Tue, 17 Jul 2012 12:14:33 +0200 Message-ID: <50053B09.2060703@redhat.com> References: <1342107302-28116-1-git-send-email-asias@redhat.com> <50052276.2080906@redhat.com> <500527BA.9000001@redhat.com> <20120717094526.GC7949@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120717094526.GC7949@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: "Michael S. Tsirkin" Cc: linux-aio@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Benjamin LaHaise , Alexander Viro , linux-fsdevel@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org Il 17/07/2012 11:45, Michael S. Tsirkin ha scritto: >> So it begs the question, is it going to be used in production, or just a >> useful reference tool? > > Sticking to raw already makes virtio-blk faster, doesn't it? > In that vhost-blk looks to me like just another optimization option. > Ideally I think user just should not care where do we handle virtio: > in-kernel or in userspace. One can imagine it being enabled/disabled > automatically if none of the features unsupported by it are used. Ok, that would make more sense. One difference between vhost-blk and vhost-net is that for vhost-blk there are also management actions that would trigger the switch, for example a live snapshot. So a prerequisite for vhost-blk would be that it is possible to disable it on the fly while the VM is running, as soon as all in-flight I/O is completed. (Note that, however, this is not possible for vhost-scsi, because it really exposes different hardware to the guest. It must not happen that a kernel upgrade or downgrade toggles between userspace SCSI and vhost-scsi, for example). >> having to >> support the API; having to handle transition from one more thing when >> something better comes out. > > Well this is true for any code. If the limited featureset which > vhost-blk can accelerate is something many people use, then accelerating > by 5-15% might outweight support costs. It is definitely what people use if they are interested in performance. Paolo From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755219Ab2GQKOp (ORCPT ); Tue, 17 Jul 2012 06:14:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51601 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751315Ab2GQKOm (ORCPT ); Tue, 17 Jul 2012 06:14:42 -0400 Message-ID: <50053B09.2060703@redhat.com> Date: Tue, 17 Jul 2012 12:14:33 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: Asias He , Stefan Hajnoczi , linux-kernel@vger.kernel.org, linux-aio@kvack.org, kvm@vger.kernel.org, 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> <20120717094526.GC7949@redhat.com> In-Reply-To: <20120717094526.GC7949@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 17/07/2012 11:45, Michael S. Tsirkin ha scritto: >> So it begs the question, is it going to be used in production, or just a >> useful reference tool? > > Sticking to raw already makes virtio-blk faster, doesn't it? > In that vhost-blk looks to me like just another optimization option. > Ideally I think user just should not care where do we handle virtio: > in-kernel or in userspace. One can imagine it being enabled/disabled > automatically if none of the features unsupported by it are used. Ok, that would make more sense. One difference between vhost-blk and vhost-net is that for vhost-blk there are also management actions that would trigger the switch, for example a live snapshot. So a prerequisite for vhost-blk would be that it is possible to disable it on the fly while the VM is running, as soon as all in-flight I/O is completed. (Note that, however, this is not possible for vhost-scsi, because it really exposes different hardware to the guest. It must not happen that a kernel upgrade or downgrade toggles between userspace SCSI and vhost-scsi, for example). >> having to >> support the API; having to handle transition from one more thing when >> something better comes out. > > Well this is true for any code. If the limited featureset which > vhost-blk can accelerate is something many people use, then accelerating > by 5-15% might outweight support costs. It is definitely what people use if they are interested in performance. Paolo