Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757534Ab2HPPWG (ORCPT ); Thu, 16 Aug 2012 11:22:06 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:39373 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755847Ab2HPPWD (ORCPT ); Thu, 16 Aug 2012 11:22:03 -0400 Message-ID: <502D100D.2030609@pobox.com> Date: Thu, 16 Aug 2012 11:21:49 -0400 From: Jeff Garzik User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: "Markus F.X.J. Oberhumer" CC: Johannes Stezenbach , linux-kernel@vger.kernel.org, Andi Kleen , chris.mason@fusionio.com, linux-btrfs@vger.kernel.org, Nitin Gupta , Richard Purdie , richard -rw- weinberger , linux-arm-kernel@lists.infradead.org Subject: Re: [GIT PULL] Update LZO compression References: <50299142.2030504@oberhumer.com> <20120814123937.GA14756@sig21.net> <502B8FE3.7080501@oberhumer.com> <20120815144539.GA8300@sig21.net> <502C92C3.7090701@oberhumer.com> In-Reply-To: <502C92C3.7090701@oberhumer.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2244 Lines: 49 On 08/16/2012 02:27 AM, Markus F.X.J. Oberhumer wrote: > On 2012-08-15 16:45, Johannes Stezenbach wrote: >> On Wed, Aug 15, 2012 at 02:02:43PM +0200, Markus F.X.J. Oberhumer wrote: >>> On 2012-08-14 14:39, Johannes Stezenbach wrote: >>>> On Tue, Aug 14, 2012 at 01:44:02AM +0200, Markus F.X.J. Oberhumer wrote: >>>>> On 2012-07-16 20:30, Markus F.X.J. Oberhumer wrote: >>>>>> >>>>>> As stated in the README this version is significantly faster (typically more >>>>>> than 2 times faster!) than the current version, has been thoroughly tested on >>>>>> x86_64/i386/powerpc platforms and is intended to get included into the >>>>>> official Linux 3.6 or 3.7 release. >>>>>> >>>>>> I encourage all compression users to test and benchmark this new version, >>>>>> and I also would ask some official LZO maintainer to convert the updated >>>>>> source files into a GIT commit and possibly push it to Linus or linux-next. >>>> >>>> Sorry for not reporting earlier, but I didn't have time to do real >>>> benchmarks, just a quick test on ARM926EJ-S using barebox, >>>> and found in the new version decompression is slower: >>>> http://lists.infradead.org/pipermail/barebox/2012-July/008268.html >>> >>> I can only guess, but maybe your ARM cpu does not have an efficient >>> implementation of {get,put}_unaligned(). >> >> Yes, ARMv5 cannot do unaligned access. ARMv6+ could, but >> I think the Linux kernel normally traps it for debug, >> all ARM seem to use generic {get,put}_unaligned() implementation >> which use byte access and shift. > > Hmm - I could imagine that we're wasting a lot of possible speed gain > by not exploiting that feature on ARMv6+. Or you could just realize that unaligned accesses are slow in the best case, and are simply not supported on some processors. If you think a little bit, I bet you could come up with a solution that operates at cacheline-aligned granularity, something that would be _even faster_ than simply fixing the code to do aligned accesses. Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/