From owner-svn-src-all@FreeBSD.ORG Thu Oct 31 20:49:18 2013 Return-Path: Delivered-To: svn-src-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id F2BB2FAE; Thu, 31 Oct 2013 20:49:17 +0000 (UTC) (envelope-from jmg@h2.funkthat.com) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id AEC66217B; Thu, 31 Oct 2013 20:49:17 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id r9VKnGTB057450 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Thu, 31 Oct 2013 13:49:17 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id r9VKnGCW057449; Thu, 31 Oct 2013 13:49:16 -0700 (PDT) (envelope-from jmg) Date: Thu, 31 Oct 2013 13:49:16 -0700 From: John-Mark Gurney To: Luigi Rizzo Subject: Re: svn commit: r257455 - head/sys/net Message-ID: <20131031204916.GF58155@funkthat.com> References: <201310311546.r9VFkAIb049844@svn.freebsd.org> <20131031180336.GA62132@onelab2.iet.unipi.it> <5272AAC4.4030700@freebsd.org> <1383247645.31172.29.camel@revolution.hippie.lan> <20131031200502.GB83212@onelab2.iet.unipi.it> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131031200502.GB83212@onelab2.iet.unipi.it> User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Thu, 31 Oct 2013 13:49:17 -0700 (PDT) Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, Andre Oppermann , Ian Lepore X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 31 Oct 2013 20:49:18 -0000 Luigi Rizzo wrote this message on Thu, Oct 31, 2013 at 21:05 +0100: > On Thu, Oct 31, 2013 at 01:27:25PM -0600, Ian Lepore wrote: > ... > > Is there any chance all this reworking might get us to a position where > > the protocol header in an mbuf doesn't have to be 32-bit aligned > > anymore? We pay a pretty heavy price for that requirement in the > > drivers of the least capable hardware we support, the systems that have > > the least horsepower to spare to make an extra copy of each packet to > > realign it. > > So are you suggesting to use some 'copy_unaligned_32()' function/macro to > access 32-bit protocol fields in the network stack ? > (16-bit entries should not be an issue) my idea has been to make a change to the various ip/tcp/udp layers that is dependant upon __NO_STRICT_ALIGNMENT and if we do require strict alignment to copy the header to a stack buffer to align the data... Apparently someone started work on this and created IP_HDR_ALIGNED_P, though it's apparently only used in if_bridge, and why it's necessary, I'm not sure... I know ARMv4 takes a serious performance hit because of this... Often the machines that doesn't support unaligned accesses also have bad DMA engines that can't do DMA to two byte boundaries forcing us to copy the packet by using bounce pages... I haven't audited AVILA to see if it has the issue, but I know that the TS-7200 port I was working on has this issue... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."