From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753843AbaG2O7N (ORCPT ); Tue, 29 Jul 2014 10:59:13 -0400 Received: from casper.infradead.org ([85.118.1.10]:37975 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751151AbaG2O7M (ORCPT ); Tue, 29 Jul 2014 10:59:12 -0400 Date: Tue, 29 Jul 2014 16:59:10 +0200 From: Peter Zijlstra To: Vincent Guittot Cc: Rik van Riel , linux-kernel , Michael Neuling , Ingo Molnar , jhladky@redhat.com, ktkhai@parallels.com, tim.c.chen@linux.intel.com, Nicolas Pitre Subject: Re: [PATCH 1/2] sched: fix and clean up calculate_imbalance Message-ID: <20140729145910.GH3935@laptop> References: <1406571388-3227-1-git-send-email-riel@redhat.com> <1406571388-3227-2-git-send-email-riel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 29, 2014 at 11:04:50AM +0200, Vincent Guittot wrote: > > In situations where all the domains are overloaded, or where only the > > busiest domain is overloaded, that code is also superfluous, since > > the normal env->imbalance calculation will figure out how much to move. > > Remove the load_above_capacity calculation. > > IMHO, we should not remove that part which is used by prefer_sibling > > Originally, we had 2 type of busiest group: overloaded or imbalanced. > You add a new one which has only a avg_load higher than other so you > should handle this new case and keep the other ones unchanged Right, so we want that code for overloaded -> overloaded migrations such as not to cause idle cpus in an attempt to balance things. Idle cpus are worse than imbalance. But in case of overloaded/imb -> !overloaded migrations we can allow it, and in fact want to allow it in order to balance idle cpus.