Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756459AbXIRJtH (ORCPT ); Tue, 18 Sep 2007 05:49:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754804AbXIRJs4 (ORCPT ); Tue, 18 Sep 2007 05:48:56 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:44345 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754729AbXIRJsz (ORCPT ); Tue, 18 Sep 2007 05:48:55 -0400 Date: Tue, 18 Sep 2007 11:48:29 +0200 From: Ingo Molnar To: Rob Hussey Cc: linux-kernel@vger.kernel.org, ck@vds.kolivas.org Subject: Re: Scheduler benchmarks - a follow-up Message-ID: <20070918094829.GA3809@elte.hu> References: <6b8cef970709170221s4301e896x2ee123a149c05c3a@mail.gmail.com> <20070917130524.GA10707@elte.hu> <20070917203607.GA20564@elte.hu> <6b8cef970709172130v317a6c48h814ef5a1488f798e@mail.gmail.com> <20070918084825.GA25803@elte.hu> <6b8cef970709180245r86d370q2b1a92a29128f2e@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6b8cef970709180245r86d370q2b1a92a29128f2e@mail.gmail.com> User-Agent: Mutt/1.5.14 (2007-02-12) 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=3.1.7-deb -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2230 Lines: 48 * Rob Hussey wrote: > On 9/18/07, Ingo Molnar wrote: > > > > * Rob Hussey wrote: > > > > > The obligatory graphs: > > > http://www.healthcarelinen.com/misc/benchmarks/BOUND_NOPREEMPT_lat_ctx_benchmark.png > > > http://www.healthcarelinen.com/misc/benchmarks/BOUND_NOPREEMPT_hackbench_benchmark.png > > > http://www.healthcarelinen.com/misc/benchmarks/BOUND_NOPREEMPT_pipe-test_benchmark.png > > > > btw., it's likely that if you turn off CONFIG_PREEMPT for .21 and for > > .22-ck1 they'll improve a bit too - so it's not fair to put the .23 > > !PREEMPT numbers on the graph as the PREEMPT numbers of the other > > kernels. (it shows the .23 scheduler being faster than it really is) > > > > The graphs are really just to show where the new numbers fit in. Plus, > I was too lazy to run all the numbers again. yeah - the graphs are completely OK (and they are really nice and useful), i just wanted to point this out for completeness. > > the pipe-test behavior looks like an outlier. !PREEMPT only removes > > code (which makes the code faster), so this could be a cache layout > > artifact. (or perhaps we preempt at a different point which is > > disadvantageous to caching?) Pipe-test is equivalent to "lat_ctx -s > > 0 2" so if there was a genuine slowdown it would show up in the > > lat_ctx graph - but the graph shows a speedup. > > Interestingly, every set of lat_ctx -s 0 2 numbers I run on the > !PREEMPT kernel are on average higher than with PREEMPT (around 2.84 > for !PREEMPT and 2.4 for PREEMPT). Anything higher than around 2 or 3 > (such as lat_ctx -s 0 8) gives lower average numbers for !PREEMPT. perhaps this 2 task ping-pong is somehow special in that it manages to fit into L1 cache much better under PREEMPT than under !PREEMPT. (usually the opposite is true) At 3 tasks or more things dont fit anymore (or the special alignment is gone) so the faster !PREEMPT code wins. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/