From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752910AbZHXRK6 (ORCPT ); Mon, 24 Aug 2009 13:10:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752894AbZHXRK5 (ORCPT ); Mon, 24 Aug 2009 13:10:57 -0400 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:58210 "EHLO e23smtp05.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752889AbZHXRK5 (ORCPT ); Mon, 24 Aug 2009 13:10:57 -0400 Date: Mon, 24 Aug 2009 22:14:52 +0530 From: Balbir Singh To: Peter Zijlstra Cc: Andreas Herrmann , Ingo Molnar , linux-kernel@vger.kernel.org, Gautham Shenoy , "svaidy@linux.vnet.ibm.com" Subject: Re: [PATCH 11/15] sched: Pass unlimited __cpu_power information to upper domain level groups Message-ID: <20090824164452.GR29572@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090820131243.GO29327@alberich.amd.com> <20090820134155.GZ29327@alberich.amd.com> <1251127297.7538.291.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1251127297.7538.291.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra [2009-08-24 17:21:37]: > On Thu, 2009-08-20 at 15:41 +0200, Andreas Herrmann wrote: > > For performance reasons __cpu_power in a sched_group might be limited > > such that the group can handle only one task. To correctly calculate > > the capacity in upper domain level groups the unlimited power > > information is required. This patch stores unlimited __cpu_power > > information in sched_groups.orig_power and uses this when calculating > > __cpu_power in upper domain level groups. > > OK, so this tries to fix the cpu_power wreckage? > > ok, so let me try this with an example: > > > Suppose we have a dual-core with shared cache and SMT > > 0-3 MC > 0-1 2-3 SMT > > Then both levels fancy setting SHARED_RESOURCES and both levels end up > normalizing the cpu_power to 1, so when we unplug cpu 2, load-balancing > gets all screwy because the whole system doesn't get normalized > properly. > > What you propose here is every time we muck with cpu_power we keep the > real stuff in orig_power and use that to compute the level above. > > Except you don't use it in the load-balancer proper, so normalization is > still hosed. > > Its a creative solution, but I'd rather see cpu_power returned to a > straight sum of actual power to normalize the inter-cpu runqueue weights > and do the placement decision using something else. The real solution is to find a way to solve asymmetric load balancing, I suppose. The asymmetry might be due to cores being hot-plugged for example -- Balbir