From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933119AbdDEM6Y (ORCPT ); Wed, 5 Apr 2017 08:58:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:32963 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932946AbdDEM5s (ORCPT ); Wed, 5 Apr 2017 08:57:48 -0400 Date: Wed, 5 Apr 2017 14:57:43 +0200 From: Michal Hocko To: Srikar Dronamraju Cc: Ingo Molnar , Peter Zijlstra , LKML , Mel Gorman , Rik van Riel Subject: Re: [PATCH] sched: Fix numabalancing to work with isolated cpus Message-ID: <20170405125743.GB7258@dhcp22.suse.cz> References: <1491326848-5748-1-git-send-email-srikar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1491326848-5748-1-git-send-email-srikar@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 04-04-17 22:57:28, Srikar Dronamraju wrote: [...] > For example: > perf bench numa mem --no-data_rand_walk -p 4 -t $THREADS -G 0 -P 3072 -T 0 -l 50 -c -s 1000 > would call sched_setaffinity that resets the cpus_allowed mask. > > Cpus_allowed_list: 0-55,57-63,65-71,73-79,81-87,89-175 > Cpus_allowed_list: 0,8,16,24,32,40,48,56,64,72,80,88,96,104,112,120,128,136,144,152,160,168 > Cpus_allowed_list: 0,8,16,24,32,40,48,56,64,72,80,88,96,104,112,120,128,136,144,152,160,168 > Cpus_allowed_list: 0,8,16,24,32,40,48,56,64,72,80,88,96,104,112,120,128,136,144,152,160,168 > Cpus_allowed_list: 0,8,16,24,32,40,48,56,64,72,80,88,96,104,112,120,128,136,144,152,160,168 > > The isolated cpus are part of the cpus allowed list. In the above case, > numabalancing ends up scheduling some of these tasks on isolated cpus. Why is this bad? If the task is allowed to run on isolated CPUs then why shouldn't its numa balancing be allowed the same? The changelog describes what but doesn't explain _why_ this change is needed/useful. -- Michal Hocko SUSE Labs