From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id AB93237B3; Fri, 4 Nov 2016 09:09:25 +0100 (CET) Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 234FF81255; Fri, 4 Nov 2016 08:09:25 +0000 (UTC) Received: from [10.36.4.213] (vpn1-4-213.ams2.redhat.com [10.36.4.213]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id uA489MwA028828 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 4 Nov 2016 04:09:24 -0400 To: Yuanhan Liu References: <1478189400-14606-1-git-send-email-yuanhan.liu@linux.intel.com> <1478189400-14606-2-git-send-email-yuanhan.liu@linux.intel.com> <915489cd-7e1a-9a0c-ab9d-780f6103501b@redhat.com> <20161104020005.GV16751@yliu-dev.sh.intel.com> Cc: dev@dpdk.org, stable@dpdk.org, Ilya Maximets From: Maxime Coquelin Message-ID: <4dec2204-4da9-da61-fbbf-d17748f2f9bc@redhat.com> Date: Fri, 4 Nov 2016 09:09:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20161104020005.GV16751@yliu-dev.sh.intel.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 04 Nov 2016 08:09:25 +0000 (UTC) Subject: Re: [dpdk-dev] [PATCH 1/8] net/virtio: revert "virtio: fix restart" X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 04 Nov 2016 08:09:26 -0000 On 11/04/2016 03:00 AM, Yuanhan Liu wrote: > On Thu, Nov 03, 2016 at 09:36:52PM +0100, Maxime Coquelin wrote: >> Hi Yuanhan, >> >> On 11/03/2016 05:09 PM, Yuanhan Liu wrote: >>> This reverts commit 9a0615af7746 ("virtio: fix restart"); conflict is >>> manually addressed. >>> >>> Kyle reported an issue with above commit >>> >>> qemu-kvm: Guest moved used index from 5 to 1 >>> >>> with following steps, >>> >>> 1) Start my virtio interfaces >>> 2) Send some traffic into/out of the interfaces >>> 3) Stop the interfaces >>> 4) Start the interfaces >>> 5) Send some more traffic >>> >>> And here are some quotes from Kyle's analysis, >>> >>> Prior to the patch, if an interface were stopped then started, without >>> restarting the application, the queues would be left as-is, because >>> hw->started would be set to 1. Now, calling stop sets hw->started to 0, >>> which means the next call to start will "touch the queues". This is the >>> unintended side-effect that causes the problem. >> >> Maybe a good idea to explain what is the problem the revert aims to fix. > > It aims to fix the issue, by "not touching the queues" on restart. > >> It does not seem to be clearly stated in the commit message. > > I was thinking the quote from Kyle is enough. How about following supplement: > > We should not touch the queues once the init is done, otherwise, the > vring state of virtio PMD driver and vhost-user would be inconsistent, > leading some issue like above. > > Thus this patch is reverted. > > Better now? Yes, this is much clearer from my PoV. Thanks! Maxime > > --yliu >