From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758736AbYEUEza (ORCPT ); Wed, 21 May 2008 00:55:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751336AbYEUEzU (ORCPT ); Wed, 21 May 2008 00:55:20 -0400 Received: from mga10.intel.com ([192.55.52.92]:35579 "EHLO fmsmga102.fm.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751024AbYEUEzT (ORCPT ); Wed, 21 May 2008 00:55:19 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.27,518,1204531200"; d="scan'208";a="566919841" Subject: Re: hackbench regression with 2.6.26-rc2 on tulsa machine From: "Zhang, Yanmin" To: Mike Galbraith Cc: Peter Zijlstra , LKML In-Reply-To: <1211275352.24305.6.camel@marge.simson.net> References: <1211270946.3177.236.camel@ymzhang> <1211275352.24305.6.camel@marge.simson.net> Content-Type: text/plain; charset=UTF-8 Date: Wed, 21 May 2008 12:54:10 +0800 Message-Id: <1211345650.3177.247.camel@ymzhang> Mime-Version: 1.0 X-Mailer: Evolution 2.21.5 (2.21.5-2.fc9) Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2008-05-20 at 11:22 +0200, Mike Galbraith wrote: > On Tue, 2008-05-20 at 16:09 +0800, Zhang, Yanmin wrote: > > Comparing with 2.6.26-rc1, hackbench has about 30% regression with 2.6.26-rc2 on my tulsa machine > > which is a netburst architecure hyper-threading x86_64. > > > > Command line to test: #hackbench 100 process 2000 > > > > With 2.6.26-rc1, it takes 30 seconds. But with 2.6.26-rc2/rc3, it takes 40 seconds. > > > > Bisect located below patch: > > 46151122e0a2e80e5a6b2889f595e371fe2b600d is first bad commit > > commit 46151122e0a2e80e5a6b2889f595e371fe2b600d > > Author: Mike Galbraith > > Date: Thu May 8 17:00:42 2008 +0200 > > > > sched: fix weight calculations > > > > The conversion between virtual and real time is as follows: > > > > dvt = rw/w * dt <=> dt = w/rw * dvt > > > > Since we want the fair sleeper granularity to be in real time, we actually > > need to do: > > > > dvt = - rw/w * l > > > > > > > > The bisect steps look stable. > > > > On my core architecure machines(stoakley and tigerton), I do see improvement instead of regression, > > like result from 31 seconds down to 28 seconds. > > > > I'm not sure if hyper-threading need more cares in this situation. > > Oh joy. I'll update my poor old P4 and see what I can duplicate this. > > Do you still have group scheduling enabled? Yes. CONFIG_GROUP_SCHED=y CONFIG_FAIR_GROUP_SCHED=y # CONFIG_RT_GROUP_SCHED is not set CONFIG_USER_SCHED=y # CONFIG_CGROUP_SCHED is not set > If so, can you turn it off > and try again? (when in doubt, grasp at any straw within reach;) I reran the test for dozeons of times. 1) Background processes have impact on the result and cause result to fluctuate with 8~9 seconds; 2) After turning off most services (background processes), the result looks stable; 3) I tested both 2.6.26-rc1 and 2.6.26-rc2 with CONFIG_GROUP_SCHED=n. the first one's result is about 30 seconds and the second one's result is about 31 seconds. So CONFIG_GROUP_SCHED is the key. The previous results wree got with turning off most background processes. I'm busy in other issues. -yanmin