From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id 991672617 for ; Tue, 5 Apr 2016 02:10:22 +0200 (CEST) Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP; 04 Apr 2016 17:10:21 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,442,1455004800"; d="scan'208";a="951644139" Received: from yliu-dev.sh.intel.com (HELO yliu-dev) ([10.239.67.191]) by fmsmga002.fm.intel.com with ESMTP; 04 Apr 2016 17:10:21 -0700 Date: Tue, 5 Apr 2016 08:11:46 +0800 From: Yuanhan Liu To: Rich Lane Cc: Thomas Monjalon , "Xie, Huawei" , dev@dpdk.org, stephen@networkplumber.org Message-ID: <20160405001146.GL3080@yliu-dev.sh.intel.com> References: <1459454476-6029-1-git-send-email-rlane@bigswitch.com> <2344074.HmCM8hzj4i@xps13> <20160404200538.GK3080@yliu-dev.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Subject: Re: [dpdk-dev] [PATCH] virtio: use zeroed memory for simple TX header 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: Tue, 05 Apr 2016 00:10:23 -0000 On Mon, Apr 04, 2016 at 03:57:11PM -0700, Rich Lane wrote: > On Mon, Apr 4, 2016 at 1:05 PM, Yuanhan Liu > wrote: > > On Mon, Apr 04, 2016 at 03:13:37PM +0200, Thomas Monjalon wrote: > > Huawei, Yuanhan, any comment? > > > > 2016-03-31 13:01, Rich Lane: > > >                             vq->vq_ring.desc[i + mid_idx].next = i; > > >                             vq->vq_ring.desc[i + mid_idx].addr = > > > -                                   vq->virtio_net_hdr_mem + > > > -                                           i * vq->hw->vtnet_hdr_size; > > > +                                   vq->virtio_net_hdr_mem; > > I could be wrong, but this looks like a special case when i == 0, > which is by no way that zeroed memory is guaranteed? Huawei, do > you have time to check this patch?  > > > This bug exists because the type of the objects pointed to by > virtio_net_hdr_mem changed in 6dc5de3a (virtio: use indirect ring elements), > but because it isn't a C pointer the compiler didn't catch the type mismatch. > We could also fix it with: > >     vq->virtio_net_hdr_mem + i * sizeof(struct virtio_tx_region) + offsetof > (struct virtio_tx_region, tx_hdr) > > Given that tx_hdr is the first member in struct virtio_tx_region, and using a > single header optimizes cache use, that simplifies to the code in my patch. It does. However, it hurts readability. > The > virtio-net header is never written to by simple TX so it remains zeroed. > > I can respin the patch using offsetof if that's preferred. Yes, please. In such way, we could also align with the setting up code at virtio_dev_queue_setup(). BTW, I have one question: will simple Tx work with indirect buf enabled? > Note that right now virtio simple TX is broken with DPDK vhost due to the flood > of error messages. Yes, we need the fix, and thanks for the catching. BTW, it's a regression fix, you'd better add a Fixline into your commit log. --yliu