From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AD2BC4332B for ; Mon, 23 Mar 2020 11:00:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 028AF2070A for ; Mon, 23 Mar 2020 11:00:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728102AbgCWLAO (ORCPT ); Mon, 23 Mar 2020 07:00:14 -0400 Received: from mx2.suse.de ([195.135.220.15]:59286 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727974AbgCWLAN (ORCPT ); Mon, 23 Mar 2020 07:00:13 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id D764AAC92; Mon, 23 Mar 2020 11:00:10 +0000 (UTC) Subject: Re: [PATCH net-next v4] xen networking: add basic XDP support for xen-netfront To: Denis Kirjanov Cc: netdev@vger.kernel.org, ilias.apalodimas@linaro.org, wei.liu@kernel.org, paul@xen.org References: <1584364176-23346-1-git-send-email-kda@linux-powerpc.org> <250783b3-4949-d00a-70e2-dbef1791a6c4@suse.com> <9eb74bee-8434-62aa-8158-bae130353670@suse.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: Date: Mon, 23 Mar 2020 12:00:09 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 23.03.20 11:49, Denis Kirjanov wrote: > On 3/23/20, Jürgen Groß wrote: >> On 23.03.20 11:15, Denis Kirjanov wrote: >>> On 3/18/20, Jürgen Groß wrote: >>>> On 18.03.20 13:50, Denis Kirjanov wrote: >>>>> On 3/18/20, Jürgen Groß wrote: >>>>>> On 16.03.20 14:09, Denis Kirjanov wrote: >>>>>>> The patch adds a basic XDP processing to xen-netfront driver. >>>>>>> >>>>>>> We ran an XDP program for an RX response received from netback >>>>>>> driver. Also we request xen-netback to adjust data offset for >>>>>>> bpf_xdp_adjust_head() header space for custom headers. >>>>>> >>>>>> This is in no way a "verbose patch descriprion". >>>>>> >>>>>> I'm missing: >>>>>> >>>>>> - Why are you doing this. "Add XDP support" is not enough, for such >>>>>> a change I'd like to see some performance numbers to get an idea >>>>>> of the improvement to expect, or which additional functionality >>>>>> for the user is available. >>>>> Ok, I'll try to measure some numbers. >>>>> >>>>>> >>>>>> - A short description for me as a Xen maintainer with only basic >>>>>> networking know-how, what XDP programs are about (a link to some >>>>>> more detailed doc is enough, of course) and how the interface >>>>>> is working (especially for switching between XDP mode and normal >>>>>> SKB processing). >>>>> >>>>> You can search for the "A practical introduction to XDP" tutorial. >>>>> Actually there is a lot of information available regarding XDP, you >>>>> can easily find it. >>>>> >>>>>> >>>>>> - A proper description of the netfront/netback communication when >>>>>> enabling or disabling XDP mode (who is doing what, is silencing >>>>>> of the virtual adapter required, ...). >>>>> Currently we need only a header offset from netback driver so that we >>>>> can >>>>> put >>>>> custom encapsulation header if required and that's done using xen bus >>>>> state switching, >>>>> so that: >>>>> - netback tells that it can adjust the header offset >>>>> - netfront part reads it >>>> >>>> Yes, but how is this synchronized with currently running network load? >>>> Assume you are starting without XDP being active and then you are >>>> activating it. How is the synchronization done from which request on >>>> the XDP headroom is available? >>> >>> Hi Jurgen, >>> >>> basically XDP is activated when you've assigned an xdp program to the >>> networking device. >>> Assigning an xdp program means that we have to adjust a pointer which >>> is RCU protected. >> >> This doesn't answer my question. >> >> You have basically two communication channels: the state of the frontend >> and backend for activation/deactivation of XDP, and the ring pages with >> the rx and tx requests and responses. How is the synchronization between >> those two channels done? So how does the other side know which of the >> packets in flight will then have XDP on or off? > > Right, > that's done in xen-netback using xenbus state: > - in xennet_xdp_set() we call xenbus_switch_state to tell xen-netback to > adjust offset for an RX response. > -xen-netback reads the value from xenstore and adjusts the offset for > xen-netback > in xenvif_rx_data_slot() using vif->xdp_enabled flag. And before that all in-flight requests in the ring pages are being processed and no new requests are guaranteed to be enqueued? Juergen