From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4255D343.2090006@yahoo.com.au> Date: Fri, 08 Apr 2005 10:41:39 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: per_cpu_pagesets degrades MPI performance References: <20050404192827.GA15142@sgi.com> <4251DE87.10002@yahoo.com.au> <20050407185226.GA23873@sgi.com> In-Reply-To: <20050407185226.GA23873@sgi.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Jack Steiner Cc: akpm@osdl.org, hugh@veritas.com, linux-mm@kvack.org, linux-ia64@vger.kernel.org List-ID: Jack Steiner wrote: > > Good idea. For the specific benchmark that I was running, batch sizes > of 0 (pcp disabled), 1, 3, 5, 7, 9, 10, 11, 13 & 15 all produced good results. > Batch sizes of 2, 4 and 8 produced horrible results. > Phew, I hope we won't have to make this a CONFIG_ option! > Surprisingly 7 was not quite as good as the other good values but I attribute that > to an anomaly of the reference pattern of the specific benchmark. > > Even more suprising (again an anomaly I think) was that a size of 13 ran > 10% faster than any of the other sizes. I reproduced this data point several > times - it is real. > Hmm. Yeah, sounds you are getting close to some "resonance" behaviour - were 7 and 13 are close to a multiple or divisor of some application or cache property. > Our next step to to run the full benchmark suite. That should happen > within 2 weeks. > > Tentatively, I'm planning to post a patch to change the batch size to > 2**n-1 but I'll wait for the results of the full benchmark. > Cool. I would consider (maybe you are) posting the patch ASAP, so you can get a wider range of testers, and Andrew can possibly put it in -mm. Just to get things happening in parallel. > I also want to finish understanding the issue of excessive memory > being trapped in the per_cpu lists. > Nutty problem, that, on a 256 node, 512 CPU system :( Thanks, Nick -- SUSE Labs, Novell Inc. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org