From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Bizon Subject: Re: alignment faults in 3.6 Date: Thu, 11 Oct 2012 12:56:10 +0200 Message-ID: <1349952970.1232.5.camel@sakura.staff.proxad.net> References: <20121005082439.GF4625@n2100.arm.linux.org.uk> <506ED18C.3010009@gmail.com> <20121005140556.GQ4625@n2100.arm.linux.org.uk> <506EEFBB.3060705@gmail.com> <507619FA.6080001@jonmasters.org> <1349949638.21172.8445.camel@edumazet-glaptop> <1349950926.21172.8521.camel@edumazet-glaptop> <20121011103257.GO4625@n2100.arm.linux.org.uk> <1349952574.21172.8604.camel@edumazet-glaptop> Reply-To: mbizon@freebox.fr Mime-Version: 1.0 Content-Type: text/plain; charset="ANSI_X3.4-1968" Content-Transfer-Encoding: 7bit Cc: Russell King - ARM Linux , =?ISO-8859-1?Q?M=E5ns_Rullg=E5rd?= , Jon Masters , netdev@vger.kernel.org, David Laight , linux-arm-kernel@lists.infradead.org To: Eric Dumazet Return-path: Received: from ns.iliad.fr ([212.27.33.1]:45250 "EHLO ns.iliad.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754536Ab2JKK4M (ORCPT ); Thu, 11 Oct 2012 06:56:12 -0400 In-Reply-To: <1349952574.21172.8604.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2012-10-11 at 12:49 +0200, Eric Dumazet wrote: > So if you have an alignment fault, thats because IP header is not > aligned on 4 bytes ? > > If so a driver is buggy and must be fixed. So a driver that does not align the ip header is buggy ? I always thought it was ok not to do so (with a potential performance penalty). I have some MIPS hardware that is not able to DMA on anything but 32bits aligned addresses (bcm63xx). I tried once to add a memcpy instead of taking unaligned faults and the result was *much slower* on a ipv4 forwarding test (which is what the hardware is used for). -- Maxime