From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965022AbVHJHQB (ORCPT ); Wed, 10 Aug 2005 03:16:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965027AbVHJHQB (ORCPT ); Wed, 10 Aug 2005 03:16:01 -0400 Received: from mx1.elte.hu ([157.181.1.137]:46777 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S965022AbVHJHQA (ORCPT ); Wed, 10 Aug 2005 03:16:00 -0400 Date: Wed, 10 Aug 2005 09:16:08 +0200 From: Ingo Molnar To: "Siddha, Suresh B" Cc: nickpiggin@yahoo.com.au, akpm@osdl.org, linux-kernel@vger.kernel.org, steiner@sgi.com, dvhltc@us.ibm.com, mbligh@mbligh.org Subject: Re: allow the load to grow upto its cpu_power (was Re: [Patch] don't kick ALB in the presence of pinned task) Message-ID: <20050810071608.GC21052@elte.hu> References: <20050801174221.B11610@unix-os.sc.intel.com> <20050802092717.GB20978@elte.hu> <20050809160813.B1938@unix-os.sc.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050809160813.B1938@unix-os.sc.intel.com> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Siddha, Suresh B wrote: > On Tue, Aug 02, 2005 at 11:27:17AM +0200, Ingo Molnar wrote: > > > > * Siddha, Suresh B wrote: > > > > > Jack Steiner brought this issue at my OLS talk. > > > > > > Take a scenario where two tasks are pinned to two HT threads in a physical > > > package. Idle packages in the system will keep kicking migration_thread > > > on the busy package with out any success. > > > > > > We will run into similar scenarios in the presence of CMP/NUMA. > > > > > > Patch appended. > > > > > > Signed-off-by: Suresh Siddha > > > > nice catch! > > > > fine for -mm, but i dont think we need this fix in 2.6.13, as the effect > > of the bug is an extra context-switch per 'CPU goes idle' event, in this > > very specific (and arguably broken) task binding scenario. > > No. This is not a broken scenario. Its possible in NUMA case aswell. > > For example, lets take two nodes each having two physical packages. > And assume that there are two tasks and both of them are on (may or > may n't be pinned) two packages in node-0 > > Todays load balance will detect that there is an imbalance between the > two nodes and will try to distribute the load between the nodes. > > In general, we should allow the load of a group to grow upto its > cpu_power and stop preventing these costly movements. > > Appended patch will fix this. I have done limited testing of this > patch. Guys with big NUMA boxes, please give this patch a try. makes sense in general - we should not try to move things around when we are under-utilized. (In theory there could be heavily fluctuating workloads which do not produce an above 100% average utilization, and which could benefit from a perfectly even distribution of tasks - but i dont think the load-balancer should care, as load-balancing is mostly a "slow" mechanism.) Again, 2.6.14 stuff. Acked-by: Ingo Molnar Ingo