From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthieu Moy Subject: Re: git bisect on multiple cores Date: Wed, 09 Apr 2008 10:07:25 +0200 Message-ID: References: <20080409071750.GA23211@diana.vm.bytemark.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: A B , git@vger.kernel.org To: Karl =?iso-8859-1?Q?Hasselstr=F6m?= X-From: git-owner@vger.kernel.org Wed Apr 09 10:09:27 2008 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 1JjVN0-0002CV-4L for gcvg-git-2@gmane.org; Wed, 09 Apr 2008 10:09:26 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752659AbYDIIIj convert rfc822-to-quoted-printable (ORCPT ); Wed, 9 Apr 2008 04:08:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752657AbYDIIIj (ORCPT ); Wed, 9 Apr 2008 04:08:39 -0400 Received: from harmonie.imag.fr ([147.171.130.40]:54313 "EHLO harmonie.imag.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752607AbYDIIIh (ORCPT ); Wed, 9 Apr 2008 04:08:37 -0400 Received: from mail-veri.imag.fr (mail-veri.imag.fr [129.88.43.52]) by harmonie.imag.fr (8.13.8/8.13.8) with ESMTP id m3987eSg016435; Wed, 9 Apr 2008 10:07:40 +0200 (CEST) Received: from bauges.imag.fr ([129.88.43.5]) by mail-veri.imag.fr with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA:32) (Exim 4.50) id 1JjVL3-0003Uz-UD; Wed, 09 Apr 2008 10:07:25 +0200 Received: from moy by bauges.imag.fr with local (Exim 4.63) (envelope-from ) id 1JjVL3-0005MQ-Rl; Wed, 09 Apr 2008 10:07:25 +0200 In-Reply-To: <20080409071750.GA23211@diana.vm.bytemark.co.uk> ("Karl =?iso-8859-1?Q?Hasselstr=F6m=22's?= message of "Wed\, 9 Apr 2008 09\:17\:50 +0200") User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.0 (harmonie.imag.fr [147.171.130.40]); Wed, 09 Apr 2008 10:07:40 +0200 (CEST) X-IMAG-MailScanner-Information: Please contact MI2S MIM for more information X-IMAG-MailScanner: Found to be clean X-IMAG-MailScanner-SpamCheck: X-IMAG-MailScanner-From: moy@imag.fr Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: Karl Hasselstr=F6m writes: > On 2008-04-08 12:58:47 +0200, A B wrote: > >> git bisect is really cool. I use it for the first time. Just a >> thought, if you have a multiple core computer, can't you make git >> build new versions in the background while testing the previuos >> version? Alright, if you build 2 versions, one of them will never be >> tested, but you will perhaps save some time by letting it build in >> the background? > > Adding parallelism to a binary search scales very badly -- I'd say > about logarithmically, but I haven't thought hard about it. If it's > possible to use the extra cores to speed up the build+test cycle, > that's vastly preferable. Probably logarithmically with the number of cores. But for reasonable machines, this number is relatively low, so the log is not so costly. =46or a binary search, using just 2 cores, you can try the next in the list in case of a "git bisect good" for example, and if the hypothesis is true, you've just gained a factor 2 (assuming it happens 50% of times, that should be a 50% speedup). Similarly, you should get a factor 2 with 3 cores. And as said before, you can also try trisection or N-section. But no, I won't claim this is simple to implement ;-). --=20 Matthieu