From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Monjalon Subject: Re: dpdk/vpp and cross-version migration for vhost Date: Mon, 28 Nov 2016 23:18:53 +0100 Message-ID: <5176838.Upmb1ZYUhB@xps13> References: <20161011173526-mutt-send-email-mst@kernel.org> <67cfb109-8729-916e-5535-80af620bafe5@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: dev@dpdk.org, "Weglicki, MichalX" , "Michael S. Tsirkin" , Stephen Hemminger , qemu-devel@nongnu.org, libvir-list@redhat.com, vpp-dev@lists.fd.io, =?ISO-8859-1?Q?Marc=2DAndr=E9?= Lureau , olivier.matz@6wind.com To: Maxime Coquelin , "Kavanagh, Mark B" , Kevin Traynor , Yuanhan Liu Return-path: Received: from mail-wj0-f175.google.com (mail-wj0-f175.google.com [209.85.210.175]) by dpdk.org (Postfix) with ESMTP id 713632C8 for ; Mon, 28 Nov 2016 23:18:55 +0100 (CET) Received: by mail-wj0-f175.google.com with SMTP id xy5so129028752wjc.0 for ; Mon, 28 Nov 2016 14:18:55 -0800 (PST) In-Reply-To: <67cfb109-8729-916e-5535-80af620bafe5@redhat.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 2016-11-28 16:28, Maxime Coquelin: > On 11/24/2016 04:24 PM, Kavanagh, Mark B wrote: > > DPDK v16.04 added support for vHost User TSO; as such, by default, > > TSO is advertised to guest devices as an available feature during > > feature negotiation with QEMU. > > However, while the vHost user backend sets up the majority of the > > mbuf fields that are required for TSO, there is still a reliance > > on the associated DPDK application (i.e. in this case OvS-DPDK) > > to set the remaining flags and/or offsets. > > Since OvS-DPDK doesn't currently provide that functionality, it is > > necessary to explicitly disable TSO; otherwise, undefined behaviour > > will ensue. > > Thanks Mark for the clarification. > > In this case, maybe we could add a DPDK build option to disable Vhost's > TSO support, that would be selected for OVS packages? Why do you prefer a build-time option rather than the run-time config with rte_vhost_feature_disable()? Because we need to lock the features? Reminder: build-time configuration options are forbidden in DPDK for such usage. It would prevent other applications from using the feature in a given distribution, just because it is not implemented in OVS. > Does that sound reasonable? Maybe I'm missing something but I feel it is more reasonnable to implement the missing code in OVS. If something is missing in DPDK, do not hesitate to request or add more helper functions.