From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752811AbZHHW1y (ORCPT ); Sat, 8 Aug 2009 18:27:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752682AbZHHW1w (ORCPT ); Sat, 8 Aug 2009 18:27:52 -0400 Received: from mx6.orcon.net.nz ([219.88.242.56]:55825 "EHLO mx6.orcon.net.nz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752668AbZHHW1v (ORCPT ); Sat, 8 Aug 2009 18:27:51 -0400 Message-ID: <4A7DFBE4.6060101@orcon.net.nz> Date: Sun, 09 Aug 2009 10:27:48 +1200 From: Michael Cree User-Agent: Mozilla-Thunderbird 2.0.0.22 (X11/20090707) MIME-Version: 1.0 To: Falk Hueffner CC: Matt Turner , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org Subject: Re: Bad Code generated from __{get,put}_unaligned functions References: <20090806183941.GA6854@minet.uni-jena.de> In-Reply-To: <20090806183941.GA6854@minet.uni-jena.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-DSPAM-Check: by mx6.orcon.net.nz on Sun, 09 Aug 2009 10:27:50 +1200 X-DSPAM-Result: Innocent X-DSPAM-Processed: Sun Aug 9 10:27:51 2009 X-DSPAM-Confidence: 0.6525 X-DSPAM-Probability: 0.0000 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Falk Hueffner wrote: > On Thu, Aug 06, 2009 at 01:56:12PM -0400, Matt Turner wrote: > >> I was researching different ways of writing unaligned load/store >> macros, so I checked how the kernel did it -- the most general way >> possible. See include/linux/unaligned.h. As such, very bad code is >> generated, for example on alpha with BWX, we can implement all these >> functions with a single instruction, whereas we get stuff like this >> generated from the generic functions. >> >> __get_unaligned_le32: >> .frame $30,0,$26,0 >> .prologue 0 >> ldbu $0,1($16) >> ldbu $1,2($16) >> ldbu $2,3($16) >> ldbu $3,0($16) >> sll $1,16,$1 >> sll $0,8,$0 >> bis $0,$1,$0 >> sll $2,24,$2 >> bis $0,$3,$0 >> bis $0,$2,$0 >> addl $31,$0,$0 >> ret $31,($26),1 >> >> 4 load byte instructions, shift, shift, or, shift, or, or, sign extend >> -- or ldl_u instruction. The code is more than doubly-bad for le64. >> >> Do we use the generic functions for a reason I don't see? It appears >> that it would be easy enough to add architecture-specific unaligned >> get/put functions in arch/*/include/asm/unaligned.h >> > > There should be no need for architecture specific code for Alpha. GCC > can generate the optimal code sequence for reads from unaligned struct > members as in linux/unaligned/packed_struct.h, and this code should be > used. So you should try to find out why it isn't. > Indeed, the above code looks like what one would expect from the routines in linux/unaligned/le_byteshift.h rather than packed_struct.h Michael.