From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752724AbbJLTwv (ORCPT ); Mon, 12 Oct 2015 15:52:51 -0400 Received: from www.linutronix.de ([62.245.132.108]:46421 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751604AbbJLTwt (ORCPT ); Mon, 12 Oct 2015 15:52:49 -0400 Date: Mon, 12 Oct 2015 21:52:08 +0200 (CEST) From: Thomas Gleixner To: Frederic Weisbecker cc: Ingo Molnar , LKML , Chris Metcalf , Peter Zijlstra , Mike Galbraith , Dave Jones , Oleg Nesterov , Christoph Lameter , Alexey Dobriyan , "Paul E . McKenney" , Rik van Riel , Andrew Morton Subject: Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" In-Reply-To: <1444663283-30068-1-git-send-email-fweisbec@gmail.com> Message-ID: References: <1444663283-30068-1-git-send-email-fweisbec@gmail.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 12 Oct 2015, Frederic Weisbecker wrote: > This reverts commit 8cb9764fc88b41db11f251e8b2a0d006578b7eb4. > > We assumed that nohz full users always want scheduler isolation on full > dynticks CPUs, therefore we included nohz full CPUs on cpu_isolated_map. > This means that tasks run by default on CPUs outside the nohz_full range > unless their affinity is explicity overwritten. > > This suits pure isolation workloads but when the machine is needed to > run common workloads, the available sets of CPUs to run common tasks > becomes reduced. > > We reach an extreme case when CONFIG_NO_HZ_FULL_ALL is enabled as it > leaves only CPU 0 for non-isolation tasks, which makes people think that > their supercomputer regressed to 90's UP. > > Some nohz full users appear to be interested in running normal workloads > either before or after an isolation workload. Nohz full isn't optimized > toward normal workloads but it's still better than UP performance. > > We are reaching a limitation in kernel presets here. Lets revert this > cpu_isolated_map inclusion and let userspace do its own scheduler > isolation using cpusets or explicit affinity settings. Acked-by: Thomas Gleixner