From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Cronenworth Subject: Re: e1000e max frame calculation Date: Mon, 06 Apr 2015 16:45:40 -0500 Message-ID: <5522FE84.6030104@cchtml.com> References: <5522B685.2030104@cchtml.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit To: netdev@vger.kernel.org Return-path: Received: from mta11.charter.net ([216.33.127.80]:43415 "EHLO mta11.charter.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752726AbbDFVpo (ORCPT ); Mon, 6 Apr 2015 17:45:44 -0400 Received: from imp11 ([10.20.200.11]) by mta11.charter.net (InterMail vM.8.01.05.09 201-2260-151-124-20120717) with ESMTP id <20150406214543.KWAM5815.mta11.charter.net@imp11> for ; Mon, 6 Apr 2015 17:45:43 -0400 Received: from impout006 ([68.114.189.21]) by mtaout005.msg.strl.va.charter.net (InterMail vM.9.00.015.01 201-2473-143-101) with ESMTP id <20150406214543.SINS1172.mtaout005.msg.strl.va.charter.net@impout006> for ; Mon, 6 Apr 2015 16:45:43 -0500 Received: from mcronenworth.nhsrx.com (unknown [63.237.119.62]) by cchtml.com (Postfix) with ESMTPSA id 45AAC1540144 for ; Mon, 6 Apr 2015 16:45:42 -0500 (CDT) In-Reply-To: <5522B685.2030104@cchtml.com> Sender: netdev-owner@vger.kernel.org List-ID: Preface: I am not here to start a discussion about header sizes or hardware limits. This is solely about the calculation used to limit a user when they pass a MTU to a driver. On 04/06/2015 11:38 AM, Michael Cronenworth wrote: > Other drivers appear to be using the "old" maximum frame calculation and can > continue to use 9000. > > Can a standard be decided upon that all drivers use or is it acceptable that one > driver "does its own thing?" To be specific here are some examples of maximum MTU calculation and their tests: sky2: user_mtu > ETH_JUMBO_MTU r8169: user_mtu < ETH_ZLEN || user_mtu > (ETH_DATA_LEN||x*1024 - ETH_HLEN - 2) igb: user_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN > MAX_JUMBO_FRAME_SIZE e1000e <3.15: user_mtu + ETH_HLEN + ETH_FCS_LEN > adapter->max_hw_frame_size; e1000e >=3.15: user_mtu + VLAN_HLEN + ETH_HLEN + ETH_FCS_LEN > adapter->max_hw_frame_size; Let's say the hardware has a limit of 4096 bytes. The user wishes to set an MTU of 4078 bytes. sky2: false, mtu is set r8169: false, mtu is set igb: true, mtu is not set e1000e <3.15: false, mtu is set e1000e <3.15: true, mtu is not set So some drivers work with the 4078 MTU and some do not. They all had the same hardware limit, but their driver's software calculated limit was different. Am I crazy? Thanks, Michael