From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by dpdk.org (Postfix) with ESMTP id F2D6C11C5 for ; Fri, 3 Jul 2015 03:53:49 +0200 (CEST) Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga103.fm.intel.com with ESMTP; 02 Jul 2015 18:53:48 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,396,1432623600"; d="scan'208";a="755204282" Received: from pgsmsx101.gar.corp.intel.com ([10.221.44.78]) by fmsmga002.fm.intel.com with ESMTP; 02 Jul 2015 18:53:47 -0700 Received: from shsmsx151.ccr.corp.intel.com (10.239.6.50) by PGSMSX101.gar.corp.intel.com (10.221.44.78) with Microsoft SMTP Server (TLS) id 14.3.224.2; Fri, 3 Jul 2015 09:53:46 +0800 Received: from shsmsx102.ccr.corp.intel.com ([169.254.2.165]) by SHSMSX151.ccr.corp.intel.com ([169.254.3.168]) with mapi id 14.03.0224.002; Fri, 3 Jul 2015 09:53:45 +0800 From: "Ouyang, Changchun" To: "Xie, Huawei" Thread-Topic: [dpdk-dev] [PATCH] virtio: fix the vq size issue Thread-Index: AQHQs9JlQEOaxBUIeEyxKL7zRjwCJJ3I8YBA Date: Fri, 3 Jul 2015 01:53:44 +0000 Message-ID: References: <1435736930-26737-1-git-send-email-changchun.ouyang@intel.com> In-Reply-To: Accept-Language: zh-CN, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH] virtio: fix the vq size issue 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, 03 Jul 2015 01:53:50 -0000 > -----Original Message----- > From: Xie, Huawei > Sent: Thursday, July 2, 2015 5:16 PM > To: Ouyang, Changchun > Cc: dev@dpdk.org; Thomas Monjalon > Subject: Re: [dpdk-dev] [PATCH] virtio: fix the vq size issue >=20 > On 7/2/2015 10:16 AM, Ouyang, Changchun wrote: > > > >> -----Original Message----- > >> From: Xie, Huawei > >> Sent: Thursday, July 2, 2015 10:02 AM > >> To: Ouyang, Changchun; dev@dpdk.org; Thomas Monjalon > >> Subject: Re: [dpdk-dev] [PATCH] virtio: fix the vq size issue > >> > >> On 7/2/2015 8:29 AM, Ouyang, Changchun wrote: > >>> Hi huawei, > >>> > >>>> -----Original Message----- > >>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Xie, Huawei > >>>> Sent: Wednesday, July 1, 2015 11:53 PM > >>>> To: dev@dpdk.org; Thomas Monjalon > >>>> Subject: Re: [dpdk-dev] [PATCH] virtio: fix the vq size issue > >>>> > >>>> On 7/1/2015 3:49 PM, Ouyang Changchun wrote: > >>>>> This commit breaks virtio basic packets rx functionality: > >>>>> d78deadae4dca240e85054bf2d604a801676becc > >>>>> > >>>>> The QEMU use 256 as default vring size, also use this default > >>>>> value to calculate the virtio avail ring base address and used > >>>>> ring base address, and vhost in the backend use the ring base > >>>>> address to do packet > >>>> IO. > >>>>> Virtio spec also says the queue size in PCI configuration is > >>>>> read-only, so virtio front end can't change it. just need use the > >>>>> read-only value to allocate space for vring and calculate the > >>>>> avail and used ring base address. Otherwise, the avail and used > >>>>> ring base > >>>> address will be different between host and guest, accordingly, > >>>> packet IO can't work normally. > >>>> virtio driver could still use the vq_size to initialize avail ring > >>>> and use ring so that they still have the same base address. > >>>> The other issue is vhost use index & (vq->size -1) to index the rin= g. > >>> I am not sure what is your clear message here, Vhost has no choice > >>> but use vq->size -1 to index the ring, It is qemu that always use > >>> 256 as the vq size, and set the avail and used ring base address, It > >>> also tells vhost the vq size is 256. > >> I mean "the same base address issue" could be resolved, but we still > >> couldn't stop vhost using idx & vq->size -1 to index the ring. > >> > > Then this patch will resolve this avail ring base address issue. > I mean different ring base isn't the root cause. The commit message which > states that this register is read only is simple and enough.=09 The direct root cause is avail ring base address issue, Virtio front end use: vring->avail =3D vring->desc + vq_size * SIZE_OF_DESC= _ELEMENT, And fill the vring->avail->avail_idx, and the ring itself. Qemu use: vring->avail =3D vring->desc + 256 * SIZE_OF_DESC_ELEMENT, And tell vhost this address, Vhost use this address to enqueue packets from= phy port into vring. Pls note that if vq_size is not 256, e.g. it is changed into 128, then the = vring->avail in host and in guest Is totally different, that is why it fail to rx any packet, because they tr= y to use different address to get Same content in that space. This is why I still think it is the root cause and I need add it into the c= ommit. >=20 > >>>> Thomas: > >>>> This fix works but introduces slight change with original code. > >>>> Could we just rollback that commit? > >>> What's your major concern for the slight change here? > >>> just removing the unnecessary check for nb_desc itself. > >>> So I think no issue for the slight change. > >> No major concern. It is better if this patch just rollbacks that > >> commit without introduce extra change if not necessary. > >> The original code set nb_desc to vq_size, though it isn't used later. > >> > > I prefer to have the slight change to remove unnecessary setting. > > > >>> Thanks > >>> Changchun > >>> > >>> > >>> > >>> > > > >