From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by dpdk.org (Postfix) with ESMTP id 65BF529C6 for ; Fri, 16 Nov 2018 11:29:49 +0100 (CET) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Nov 2018 02:29:48 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,239,1539673200"; d="scan'208";a="105111810" Received: from aburakov-mobl1.ger.corp.intel.com (HELO [10.237.220.124]) ([10.237.220.124]) by fmsmga002.fm.intel.com with ESMTP; 16 Nov 2018 02:29:47 -0800 To: "Lam, Tiago" , dev@dpdk.org Cc: linville@tuxdriver.com References: <24eb3e7e-17f9-222f-aab1-5acfb86823c7@intel.com> From: "Burakov, Anatoly" Message-ID: <4b9be9f2-b1a2-df99-7c76-41b54d0cfdf4@intel.com> Date: Fri, 16 Nov 2018 10:29:46 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <24eb3e7e-17f9-222f-aab1-5acfb86823c7@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] af_packet dev default "framesz" of 2048B X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Nov 2018 10:29:49 -0000 On 15-Nov-18 7:02 PM, Lam, Tiago wrote: > Hi guys, > > OvS-DPDK has recently had small a change that changed the data room > available in an mbuf (commit dfaf00e in OvS). This seems to have had the > consequence of breaking the initialisation of eth_af_packets interfaces, > when using default values ("options:dpdk- > devargs=eth_af_packet0,iface=enp61s0f3"). > > After investigating, what seems to be happening is that the > eth_af_packet dev expects an available space of "2048B - TPACKET2_HDRLEN > + sizeof(struct sockaddr_ll) = 2016B" to be available in the data room > of each mbuf. Previous to the above commit, OvS would allocate some > extra space, and this would mean there would be enough room for the > checks performed in eth_rx_queue_setup() and eth_dev_mtu_set() in > rte_eth_af_packet.c. However, with the recent commit that isn't the case > anymore, and without that extra space the first check in > eth_rx_queue_setup() will now be hit and setup of a eth_af_packet > interface fails. > > What I'm trying to understand here is, the logic behind setting a > default 'framesz' of 2048B and it being hardcoded (instead of being > based on the underlying MTU of the interface, or the mbuf data room > directly). The documentation in [1] for mmap() and setting up buffer > rings mentions the exact same values > (tp_block_size=4096,tp_frame_size=2048), which seem to have been > introduced on the first commit, back in 2014. The only constraint > for the framesize, it seems, its that it fits inside the blocksize (i.e. > doesn't span multiple blocksizes), and is aligned to TPACKET_ALIGNMENT. I think the reason is no one bothered to do it properly (same with detecting NUMA node locality for AF_PACKET interfaces - they all report as being on socket 0, even though it's possible to get this info from sysfs and set it correctly). -- Thanks, Anatoly