From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Hommey Subject: Re: Why Git is so fast Date: Fri, 1 May 2009 11:42:21 +0200 Message-ID: <20090501094221.GB13264@glandium.org> References: <46a038f90904270155i6c802fceoffc73eb5ab57130e@mail.gmail.com> <200904301728.06989.jnareb@gmail.com> <20090430185244.GR23604@spearce.org> <86iqkllw0c.fsf@broadpark.no> <20090501052434.GA4750@dpotapov.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Kjetil Barvik , "Shawn O. Pearce" , git@vger.kernel.org To: Dmitry Potapov X-From: git-owner@vger.kernel.org Fri May 01 11:42:34 2009 Return-path: Envelope-to: gcvg-git-2@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1LzpGL-000113-U7 for gcvg-git-2@gmane.org; Fri, 01 May 2009 11:42:34 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754231AbZEAJmZ (ORCPT ); Fri, 1 May 2009 05:42:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753936AbZEAJmZ (ORCPT ); Fri, 1 May 2009 05:42:25 -0400 Received: from vuizook.err.no ([85.19.221.46]:56842 "EHLO vuizook.err.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753118AbZEAJmZ (ORCPT ); Fri, 1 May 2009 05:42:25 -0400 Received: from cha92-13-88-165-248-19.fbx.proxad.net ([88.165.248.19] helo=jigen) by vuizook.err.no with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.69) (envelope-from ) id 1LzpG8-0007w3-19; Fri, 01 May 2009 11:42:22 +0200 Received: from mh by jigen with local (Exim 4.69) (envelope-from ) id 1LzpG9-0003Td-5f; Fri, 01 May 2009 11:42:21 +0200 Content-Disposition: inline In-Reply-To: <20090501052434.GA4750@dpotapov.dyndns.org> X-GPG-Fingerprint: A479 A824 265C B2A5 FC54 8D1E DE4B DA2C 54FD 2A58 User-Agent: Mutt/1.5.18 (2008-05-17) X-Spam-Status: (score 0.1): No, score=0.1 required=5.0 tests=RDNS_DYNAMIC autolearn=disabled version=3.2.4 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: On Fri, May 01, 2009 at 09:24:34AM +0400, Dmitry Potapov wrote: > On Thu, Apr 30, 2009 at 10:36:03PM +0200, Kjetil Barvik wrote: > > 4) The "static inline void hashcpy(....)" in cache.h could then > > maybe be written like this: > > > > static inline void hashcpy(unsigned long sha_dst[5], const unsigned long sha_src[5]) > > { > > sha_dst[0] = sha_src[0]; > > sha_dst[1] = sha_src[1]; > > sha_dst[2] = sha_src[2]; > > sha_dst[3] = sha_src[3]; > > sha_dst[4] = sha_src[4]; > > } > > > > And hopefully will be compiled to just 5 store/more > > instructions, or at least hopefully be faster than the currently > > memcpy() call. But mabye we get more compiled instructions compared > > to a single call to memcpy()? > > Good compilers can inline memcpy and should produce more efficient code > for the target architecture, which can be faster than manually written. > On x86_64, memcpy() requires only 3 load/store operations to copy SHA-1 > while the above code requires 5 operations. I guess, though, that some enforced alignment could help produce slightly more efficient code on some architectures (most notably sparc, which really doesn't like to deal with unaligned words). Mike