From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH v2 0/5] virtio: Tx performance improvements Date: Tue, 27 Oct 2015 08:52:12 +0900 Message-ID: <20151027085212.24ce7e5e@samsung9> References: <1445231772-17467-1-git-send-email-stephen@networkplumber.org> <1536056.KWEakoJpBK@xps13> <20151022090459.68015713@xeon-e3> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" To: "Xie, Huawei" Return-path: Received: from mail-pa0-f54.google.com (mail-pa0-f54.google.com [209.85.220.54]) by dpdk.org (Postfix) with ESMTP id DCCF88D8A for ; Tue, 27 Oct 2015 00:52:20 +0100 (CET) Received: by pasz6 with SMTP id z6so202146701pas.2 for ; Mon, 26 Oct 2015 16:52:20 -0700 (PDT) In-Reply-To: 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" On Fri, 23 Oct 2015 09:00:38 +0000 "Xie, Huawei" wrote: > >> Why use merge-able rx header here in the tx region? > > If mergeable rx is negotiated then the header must be used for > > both Tx and Rx. I chose to allocate the largest possible header > > needed, rather than having to deal with variable size data structure. > Our original code is also using merge-able header for TX descriptor if > this negotiated. > I checked the virtio spec, all of the merge-able header is about > receiving buffers, which is expected. That is why i feel weird here. > Maybe not a big deal? Since num_buffers is only in merge-able header, the negotiation is implied to be symmetric. Reading 0.95 spec Under "Packet Transmission" 3. If the driver negotatied the VIRTIO_NET_F_MGR_RXBUF feature the num_buffers field is set to zero.