From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753212AbbBXOWW (ORCPT ); Tue, 24 Feb 2015 09:22:22 -0500 Received: from mail-wi0-f171.google.com ([209.85.212.171]:56401 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752401AbbBXOWT (ORCPT ); Tue, 24 Feb 2015 09:22:19 -0500 Message-ID: <1424787736.5419.13.camel@gmail.com> Subject: Re: [PATCH 0/2] cpusets,isolcpus: resolve conflict between cpusets and isolcpus From: Mike Galbraith To: Rik van Riel Cc: linux-kernel@vger.kernel.org Date: Tue, 24 Feb 2015 15:22:16 +0100 In-Reply-To: <54EC86F0.8080107@redhat.com> References: <1424727906-4460-1-git-send-email-riel@redhat.com> <1424744326.10678.4.camel@gmail.com> <54EC86F0.8080107@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2015-02-24 at 09:13 -0500, Rik van Riel wrote: > On 02/23/2015 09:18 PM, Mike Galbraith wrote: > > On Mon, 2015-02-23 at 16:45 -0500, riel@redhat.com wrote: > >> Ensure that cpus specified with the isolcpus= boot commandline > >> option stay outside of the load balancing in the kernel > >> scheduler. > >> > >> Operations like load balancing can introduce unwanted latencies, > >> which is exactly what the isolcpus= commandline is there to > >> prevent. > >> > >> Previously, simply creating a new cpuset, without even touching > >> the cpuset.cpus field inside the new cpuset, would undo the > >> effects of isolcpus=, by creating a scheduler domain spanning the > >> whole system, and setting up load balancing inside that domain. > >> The cpuset root cpuset.cpus file is read-only, so there was not > >> even a way to undo that effect. > >> > >> This does not impact the majority of cpusets users, since > >> isolcpus= is a fairly specialized feature used for realtime > >> purposes. > > > > 3/3: nohz_full cpus become part of that unified isolated map? > > There may be use cases where users want nohz_full, but still > want the scheduler to automatically load balance the CPU. > > I am not sure whether we want nohz_full and isolcpus to always > overlap 100%. > > On the other hand, any CPU that is isolated with isolcpus= > probably wants nohz_full... I can't imagine caring deeply about the tiny interference of the tick, yet not caring about the massive interference of load balancing. -Mike