From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265623AbUBFSjy (ORCPT ); Fri, 6 Feb 2004 13:39:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265636AbUBFSjy (ORCPT ); Fri, 6 Feb 2004 13:39:54 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.105]:20910 "EHLO e5.ny.us.ibm.com") by vger.kernel.org with ESMTP id S265623AbUBFSjv (ORCPT ); Fri, 6 Feb 2004 13:39:51 -0500 Date: Fri, 06 Feb 2004 10:39:31 -0800 From: "Martin J. Bligh" To: Rick Lindsley , Anton Blanchard cc: piggin@cyberone.com.au, akpm@osdl.org, linux-kernel@vger.kernel.org, dvhltc@us.ibm.com Subject: Re: [PATCH] Load balancing problem in 2.6.2-mm1 Message-ID: <207100000.1076092771@flay> In-Reply-To: <200402061815.i16IFhY07073@owlet.beaverton.ibm.com> References: <200402061815.i16IFhY07073@owlet.beaverton.ibm.com> X-Mailer: Mulberry/2.1.2 (Linux/x86) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > Good stuff, I just gave the patch a spin and things seem a little > calmer. However Im still seeing a lot of balancing going on within a > node. > > This is a clearly recognizable edge case, so I'll try drawing this up on > some paper and see if I can suggest another patch. There's no good reason > to move one lone process from a particular processor to another idle one. > > But it also approaches a question that's come up before: if you have 2 > tasks on processor A and 1 on processor B, do you move one from A to B? > One argument is that the two tasks on A will take twice as long as > the one on B if you do nothing. But another says that bouncing a task > around can't correct the overall imbalance and so is wasteful. I know > of benchmarks where both behaviors are considered important. Thoughts? It's the classic fairness vs throughput thing we've argued about before. Most workloads don't have that static a number of processes, but it probably does need to do it if the imbalance is persistent ... but much more reluctantly than normal balancing. See the patch I sent out a bit earlier to test it - that may be *too* extreme in the other direction, but it should confirm what's going on, at least. M.