From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Rast Subject: Re: "git grep" parallelism question Date: Sat, 27 Apr 2013 15:46:08 +0200 Message-ID: <87mwskf5nj.fsf@hexa.v.cablecom.net> References: <7vr4hxw2mp.fsf@alter.siamese.dyndns.org> <7vip39w14d.fsf@alter.siamese.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain Cc: Junio C Hamano , Git Mailing List , =?utf-8?B?Tmd1eeG7hW4gVGjDoWkgTmfhu41j?= Duy To: Linus Torvalds X-From: git-owner@vger.kernel.org Sat Apr 27 15:46:17 2013 Return-path: Envelope-to: gcvg-git-2@plane.gmane.org Received: from vger.kernel.org ([209.132.180.67]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UW5SC-00074d-Gl for gcvg-git-2@plane.gmane.org; Sat, 27 Apr 2013 15:46:16 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753854Ab3D0NqM (ORCPT ); Sat, 27 Apr 2013 09:46:12 -0400 Received: from edge10.ethz.ch ([82.130.75.186]:9978 "EHLO edge10.ethz.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752492Ab3D0NqL (ORCPT ); Sat, 27 Apr 2013 09:46:11 -0400 Received: from CAS12.d.ethz.ch (172.31.38.212) by edge10.ethz.ch (82.130.75.186) with Microsoft SMTP Server (TLS) id 14.2.298.4; Sat, 27 Apr 2013 15:46:05 +0200 Received: from hexa.v.cablecom.net.ethz.ch (46.126.8.85) by CAS12.d.ethz.ch (172.31.38.212) with Microsoft SMTP Server (TLS) id 14.2.298.4; Sat, 27 Apr 2013 15:46:08 +0200 In-Reply-To: (Linus Torvalds's message of "Fri, 26 Apr 2013 13:31:41 -0700") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) X-Originating-IP: [46.126.8.85] Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: Linus Torvalds writes: > Anyway, I think your patch is good if for no other reason that it > allows this kind of testing, but at least for my machine, clearly the > current default of eight threads is actually "good enough". Maybe > somebody with a very different machine might want to run the above > script and see if how sensitive other machines are to this parameter.. I think the last time Duy, Peff, me and others looked into grep threading (which was a while ago) we basically reached the conclusion that it's very unstable across machines. Back then I tested things on a 2x6-core Xeon OS X machine and there the performance (for the hot-cache, worktree case, which should parallelize nicely) flatlines at 5 threads for no apparent reason. -- Thomas Rast trast@{inf,student}.ethz.ch