From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755986AbYANWnR (ORCPT ); Mon, 14 Jan 2008 17:43:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750982AbYANWnC (ORCPT ); Mon, 14 Jan 2008 17:43:02 -0500 Received: from wx-out-0506.google.com ([66.249.82.234]:48218 "EHLO wx-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750921AbYANWnA (ORCPT ); Mon, 14 Jan 2008 17:43:00 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=IxLp49bcfdpRCwT6RLtCFJvs1aP5o6k7ryJtkiWLdXysEak+RY9V27q5SfQ7KsYIKYASuZKjMXYlru4tTo17ivqudxoDhUs2dJLTKmOviupP1fA3DNvhhA3hByaIIB1Bbgpt8O8g9X3+uUS/1q2ZTHMy9XyCT6wQFPPbEwcLu94= Message-ID: Date: Mon, 14 Jan 2008 22:42:54 +0000 From: "Colin Fowler" To: "Ingo Molnar" Subject: Re: Performance loss 2.6.22->22.6.23->2.6.24-rc7 on CPU intensive benchmark on 8 Core Xeon Cc: linux-kernel@vger.kernel.org, "Peter Zijlstra" In-Reply-To: <20080114185520.GA26540@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080114185520.GA26540@elte.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ingo, thanks for the reply. Modifying /proc/sys/kernel/sched_latency_ns to be double may have in fact made things slightly worse. I used 24-rc7 Your script was only written to run for 15 seconds, so I ran it so it multiple times so it covered most of the benchmark. Other issues with these data may be that for much of the benchmark I am building data structures utilizing at most 1 to 3 cores. I'm not concerned with these timings personally as this is considered the offline part of the render. Once these data structures are built I proceed to render across 8 cores. This is the section of the benchmark I get my timings from ( I use RDTSC before and after the render segment). The majority of the overall time taken for a run is therefore data structure building. I do not time this. Colin. On Jan 14, 2008 6:55 PM, Ingo Molnar wrote: > > * 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 >