From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756825Ab2IDLSq (ORCPT ); Tue, 4 Sep 2012 07:18:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:19107 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756782Ab2IDLSo (ORCPT ); Tue, 4 Sep 2012 07:18:44 -0400 Message-ID: <5045E387.4030103@redhat.com> Date: Tue, 04 Sep 2012 13:18:31 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: "Nicholas A. Bellinger" , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, kvm@vger.kernel.org, rusty@rustcorp.com.au, jasowang@redhat.com, virtualization@lists.linux-foundation.org, Christoph Hellwig , Jens Axboe , target-devel Subject: Re: [PATCH 5/5] virtio-scsi: introduce multiqueue support References: <1346154857-12487-1-git-send-email-pbonzini@redhat.com> <1346154857-12487-6-git-send-email-pbonzini@redhat.com> <1346725294.4162.79.camel@haakon2.linux-iscsi.org> <5045A3B4.2030101@redhat.com> <20120904084628.GA8437@redhat.com> <5045D6FF.5020801@redhat.com> <20120904110905.GA9119@redhat.com> In-Reply-To: <20120904110905.GA9119@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 04/09/2012 13:09, Michael S. Tsirkin ha scritto: >> > queuecommand on CPU #0 queuecommand #2 on CPU #1 >> > -------------------------------------------------------------- >> > atomic_inc_return(...) == 1 >> > atomic_inc_return(...) == 2 >> > virtscsi_queuecommand to queue #1 >> > tgt->req_vq = queue #0 >> > virtscsi_queuecommand to queue #0 >> > >> > then two requests are issued to different queues without a quiescent >> > point in the middle. > What happens then? Does this break correctness? Yes, requests to the same target should be processed in FIFO order, or you have things like a flush issued before the write it was supposed to flush. This is why I can only change the queue when there is no request pending. Paolo