From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <stephen@networkplumber.org>
Received: from mail-ig0-f179.google.com (mail-ig0-f179.google.com
 [209.85.213.179]) by dpdk.org (Postfix) with ESMTP id 023D58D3D
 for <dev@dpdk.org>; Tue, 27 Oct 2015 03:23:46 +0100 (CET)
Received: by igpw7 with SMTP id w7so102213igp.1
 for <dev@dpdk.org>; Mon, 26 Oct 2015 19:23:45 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=networkplumber_org.20150623.gappssmtp.com; s=20150623;
 h=mime-version:in-reply-to:references:date:message-id:subject:from:to
 :cc:content-type;
 bh=PHKZgCLL3rmFjb1nt71FS1/BTT5InrPeb4/w9ERB0mg=;
 b=ab4Qd4Zdt6QBwCKcB3kCDMk3Y4UY0qBzlEgNQTiGJkkOG+oUAJn//dYbsaMraaMpr7
 u9+4rZ/N9dJnN+MOUEcOuziLBqzAQzRF4Q1hREqgSjPUXZXuT8C+PbJjxw75OB22rvMC
 ZjFrDqde/hEwSO2uwWxzvkzA2aaxlDwcKUdNdw/t3/eBFt/00LwOn/uLRqSyIPfNZS7T
 0J0rJtSA543+S2GY1VsIE3Yaavnziq+qcjRSNOnmGwd43bPg8RK6LaupWcYTrOP3lvCH
 pd7ygSTCM7BveF71gXP1JINFOoXfEm2830MoySBLuig3kalT7TnpWaK9svfqo+ENY9fS
 sxBg==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20130820;
 h=x-gm-message-state:mime-version:in-reply-to:references:date
 :message-id:subject:from:to:cc:content-type;
 bh=PHKZgCLL3rmFjb1nt71FS1/BTT5InrPeb4/w9ERB0mg=;
 b=g+wusoWD91jt4VUYcg1kuMr+EBWDZgzksSWnOFizm/MypjGYj7Yv3keuDiB5Yb/4DZ
 z6xbXTrFmkWJ3TDGmwial3t9yKvKT4DFcAJuiSV4n6RvY6za245GI8q+9hIjkfutetGX
 BoCyGwfHwRyhcDcTOtmGlKq/kf9uEdYJ9wqoKzH6MF0h9lY0KVKUhTmLUaSWGERNsisC
 v56Atx4h/7tRXs1kSPGDJoS9DwCdX2/EJESB9xhwi0aDUmAI/izgbu/79rPwdNhvjk6/
 JpTE+pPoUAUhu7qOm9TUccDOB8PMD3fb65og+ZQqzVdqEgq6NdmMguL3mESwe8GuM3YP
 ySaQ==
X-Gm-Message-State: ALoCoQkAUcJwYty4xPfF2DvRpYVn4In3xxnwPAkzkSA7xjj8Mj80zGRuJzMxeCGwivFiq2qepYtN
MIME-Version: 1.0
X-Received: by 10.50.83.104 with SMTP id p8mr22377741igy.13.1445912625419;
 Mon, 26 Oct 2015 19:23:45 -0700 (PDT)
Received: by 10.64.123.164 with HTTP; Mon, 26 Oct 2015 19:23:45 -0700 (PDT)
In-Reply-To: <C37D651A908B024F974696C65296B57B4B144C55@SHSMSX101.ccr.corp.intel.com>
References: <1445231772-17467-1-git-send-email-stephen@networkplumber.org>
 <1536056.KWEakoJpBK@xps13>
 <C37D651A908B024F974696C65296B57B4B137003@SHSMSX101.ccr.corp.intel.com>
 <20151022090459.68015713@xeon-e3>
 <C37D651A908B024F974696C65296B57B4B13AC87@SHSMSX101.ccr.corp.intel.com>
 <20151027085212.24ce7e5e@samsung9>
 <C37D651A908B024F974696C65296B57B4B144C55@SHSMSX101.ccr.corp.intel.com>
Date: Tue, 27 Oct 2015 11:23:45 +0900
Message-ID: <CAOaVG15O59cJc7ktFczr5cLCeNLo2zY5Md-ab56ZA3Q2RP6v9w@mail.gmail.com>
From: Stephen Hemminger <stephen@networkplumber.org>
To: "Xie, Huawei" <huawei.xie@intel.com>
Content-Type: text/plain; charset=UTF-8
X-Content-Filtered-By: Mailman/MimeDel 2.1.15
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v2 0/5] virtio: Tx performance improvements
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
X-List-Received-Date: Tue, 27 Oct 2015 02:23:46 -0000

You need to use the extended mergeable rx buffer format.
It is a virtio spec requirement, look at Linux virtio network driver or ask
the virtio maintainers for Linux
if you need more clarification.

On Tue, Oct 27, 2015 at 10:56 AM, Xie, Huawei <huawei.xie@intel.com> wrote:

> On 10/27/2015 7:52 AM, Stephen Hemminger wrote:
> > On Fri, 23 Oct 2015 09:00:38 +0000
> > "Xie, Huawei" <huawei.xie@intel.com> 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.
> >
> Can we come to the conclusion that in tx case, we use merge-able header
> though number_buffers is not used at all?
> > 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.
> >
> >
>
>