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=-2.2 required=3.0 tests=FROM_EXCESS_BASE64, 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 9F40FC5B57A for ; Fri, 28 Jun 2019 16:51:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 827E7208E3 for ; Fri, 28 Jun 2019 16:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726812AbfF1Qvr (ORCPT ); Fri, 28 Jun 2019 12:51:47 -0400 Received: from mga11.intel.com ([192.55.52.93]:37202 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726618AbfF1Qvq (ORCPT ); Fri, 28 Jun 2019 12:51:46 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Jun 2019 09:51:46 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,428,1557212400"; d="scan'208";a="361569713" Received: from rploss-mobl1.ger.corp.intel.com (HELO btopel-mobl.ger.intel.com) ([10.252.49.216]) by fmsmga006.fm.intel.com with ESMTP; 28 Jun 2019 09:51:39 -0700 Subject: Re: [PATCH 00/11] XDP unaligned chunk placement support To: "Laatz, Kevin" , Jakub Kicinski Cc: Jonathan Lemon , netdev@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, magnus.karlsson@intel.com, bpf@vger.kernel.org, intel-wired-lan@lists.osuosl.org, bruce.richardson@intel.com, ciara.loftus@intel.com References: <20190620083924.1996-1-kevin.laatz@intel.com> <20190627142534.4f4b8995@cakuba.netronome.com> From: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Message-ID: Date: Fri, 28 Jun 2019 18:51:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1 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 2019-06-28 18:19, Laatz, Kevin wrote: > On 27/06/2019 22:25, Jakub Kicinski wrote: >> On Thu, 27 Jun 2019 12:14:50 +0100, Laatz, Kevin wrote: >>> On the application side (xdpsock), we don't have to worry about the user >>> defined headroom, since it is 0, so we only need to account for the >>> XDP_PACKET_HEADROOM when computing the original address (in the default >>> scenario). >> That assumes specific layout for the data inside the buffer.  Some NICs >> will prepend information like timestamp to the packet, meaning the >> packet would start at offset XDP_PACKET_HEADROOM + metadata len.. > > Yes, if NICs prepend extra data to the packet that would be a problem for > using this feature in isolation. However, if we also add in support for > in-order > RX and TX rings, that would no longer be an issue. However, even for NICs > which do prepend data, this patchset should not break anything that is > currently > working. (Late on the ball. I'm in vacation mode.) In your example Jakub, how would this look in XDP? Wouldn't the timestamp be part of the metadata (xdp_md.data_meta)? Isn't data-data_meta (if valid) <= XDP_PACKET_HEADROOM? That was my assumption. There were some discussion on having meta data length in the struct xdp_desc, before AF_XDP was merged, but the conclusion was that this was *not* needed, because AF_XDP and the XDP program had an implicit contract. If you're running AF_XDP, you also have an XDP program running and you can determine the meta data length (and also getting back the original buffer). So, today in AF_XDP if XDP metadata is added, the userland application can look it up before the xdp_desc.addr (just like regular XDP), and how the XDP/AF_XDP application determines length/layout of the metadata i out-of-band/not specified. This is a bit messy/handwavy TBH, so maybe adding the length to the descriptor *is* a good idea (extending the options part of the xdp_desc)? Less clean though. OTOH the layout of the meta data still need to be determined. Björn