From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752309AbYANSzk (ORCPT ); Mon, 14 Jan 2008 13:55:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750966AbYANSzd (ORCPT ); Mon, 14 Jan 2008 13:55:33 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:46254 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750708AbYANSzc (ORCPT ); Mon, 14 Jan 2008 13:55:32 -0500 Date: Mon, 14 Jan 2008 19:55:20 +0100 From: Ingo Molnar To: Colin Fowler Cc: linux-kernel@vger.kernel.org, Peter Zijlstra Subject: Re: Performance loss 2.6.22->22.6.23->2.6.24-rc7 on CPU intensive benchmark on 8 Core Xeon Message-ID: <20080114185520.GA26540@elte.hu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Colin Fowler wrote: > Benchmark : A ray-trace is performed on 500 times on 17 separate > scenes. Workload is distributed by tiling the framebuffer into N 32x32 > pixel tiles. Each CPU grabs one of N tiles out of the queue and > repeats until no jobs are left. Rendering is to a shared framebuffer > (obviously this causes problems with caching). Locking and > synchronization is done using pthreads. > > Other details: The system is cleanly booted for each run. No I/O is > performed during the timed portions of the test. The benchmark does > however read a model file from the drive and build a data structure > from it before each timed portion. > > On the 2.6.22 series of kernels results are pretty much the same. On > 2.6.23 series kernels I see a loss in speed of ~2% across the board. > On 2.6.24-rc7 that loss in speed is perhaps very slightly worse (~3%). > 2.6.22 Kernels tested: 22.9(Ubuntu Stock Kernel), 22.14, 22.15 > 2.6.23 Kernels tested: 23.1, 23.3, 23.13 > 2.6.24 Kernels tested: 24-rc7 > > I have my kernel compiled to use the SLAB allocator. All other > tweaking options are set as defaults. My config files are available at > http://vangogh.cs.tcd.ie/fowler/configs . Perhaps I'm configuring > something wrong for the type of work I do? Could you try CONFIG_SCHED_DEBUG=y and CONFIG_SCHEDSTATS=y and double the value of /proc/sys/kernel/sched_latency_ns - does that make any difference? Please also run the following script while the ray-trace app is running: http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh and send me the output of it, so that we can have an idea about what's going on in your system during this workload. Ingo