From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752022AbbJLPVa (ORCPT ); Mon, 12 Oct 2015 11:21:30 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:38174 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751451AbbJLPV2 (ORCPT ); Mon, 12 Oct 2015 11:21:28 -0400 From: Frederic Weisbecker To: Ingo Molnar Cc: LKML , Frederic Weisbecker , Chris Metcalf , Peter Zijlstra , Mike Galbraith , Dave Jones , Thomas Gleixner , Oleg Nesterov , Christoph Lameter , Alexey Dobriyan , "Paul E . McKenney" , Rik van Riel , Andrew Morton Subject: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Date: Mon, 12 Oct 2015 17:21:23 +0200 Message-Id: <1444663283-30068-1-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 2.5.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Reported-by: Ingo Molnar Reported-by: Mike Galbraith Cc: Chris Metcalf Cc: Rik van Riel Cc: Christoph Lameter Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Dave Jones Cc: Oleg Nesterov Cc: Paul E. McKenney Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Alexey Dobriyan Cc: Andrew Morton Signed-off-by: Frederic Weisbecker --- kernel/sched/core.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6159531..3c35b5f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7238,9 +7238,6 @@ void __init sched_init_smp(void) alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL); alloc_cpumask_var(&fallback_doms, GFP_KERNEL); - /* nohz_full won't take effect without isolating the cpus. */ - tick_nohz_full_add_cpus_to(cpu_isolated_map); - sched_init_numa(); /* -- 2.5.3