From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754065AbaGPWhs (ORCPT ); Wed, 16 Jul 2014 18:37:48 -0400 Received: from mail-yh0-f45.google.com ([209.85.213.45]:39063 "EHLO mail-yh0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752554AbaGPWhp (ORCPT ); Wed, 16 Jul 2014 18:37:45 -0400 From: Pranith Kumar To: "Paul E. McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Andrew Morton , Frederic Weisbecker , Michal Hocko , Matt Turner , Paul Gortmaker , =?UTF-8?q?=E8=94=A1=E6=AD=A3=E9=BE=99?= , Kevin Hilman , Tejun Heo , Fabian Frederick , David Howells , Peter Foley , Eric Paris , Dwight Engen , "Eric W. Biederman" , "H. Peter Anvin" , linux-kernel@vger.kernel.org (open list) Subject: [RFC PATCH 1/1] rcu: Allow user to ovveride RCU_NOCB_CPU_ALL at boot time Date: Wed, 16 Jul 2014 18:38:08 -0400 Message-Id: <1405550289-18020-1-git-send-email-bobby.prani@gmail.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A kernel built with RCU_NOCB_CPU_ALL build time option will offload callbacks from all CPUs. The user cannot override this behavior without recompiling the kernel with the RCU_NOCB_CPU_ALL option turned off. This commit allows the user to override the build-time option by using the rcu_nocbs= boot time option without needing to recompile the kernel. Please note that this is how NO_HZ_FULL_ALL build time option works and this commit makes it work similar to that. Signed-off-by: Pranith Kumar --- init/Kconfig | 14 +++++++------- kernel/rcu/tree_plugin.h | 8 ++++---- 2 files changed, 11 insertions(+), 11 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 41066e4..7d363a4 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -768,13 +768,13 @@ config RCU_NOCB_CPU_ALL bool "All CPUs are build_forced no-CBs CPUs" depends on RCU_NOCB_CPU help - This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs= - boot parameter will be ignored. All CPUs' RCU callbacks will - be executed in the context of per-CPU rcuo kthreads created for - this purpose. Assuming that the kthreads whose names start with - "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter - on the remaining CPUs, but might decrease memory locality during - RCU-callback invocation, thus potentially degrading throughput. + If the user doesn't pass the rcu_nocbs= boot option, force all CPUs + to be no-CBs CPUs. All CPUs' RCU callbacks will be executed in the + context of per-CPU rcuo kthreads created for this purpose. Assuming + that the kthreads whose names start with "rcuo" are bound to + "housekeeping" CPUs, this reduces OS jitter on the remaining CPUs, but + might decrease memory locality during RCU-callback invocation, thus + potentially degrading throughput. Select this if all CPUs need to be no-CBs CPUs for real-time or energy-efficiency reasons. diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index a2113f6..b97a939 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -92,15 +92,15 @@ static void __init rcu_bootup_announce_oddness(void) if (!have_rcu_nocb_mask) { zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL); have_rcu_nocb_mask = true; +#ifdef CONFIG_RCU_NOCB_CPU_ALL + pr_info("\tOffload RCU callbacks from all CPUs\n"); + cpumask_copy(rcu_nocb_mask, cpu_possible_mask); +#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ } #ifdef CONFIG_RCU_NOCB_CPU_ZERO pr_info("\tOffload RCU callbacks from CPU 0\n"); cpumask_set_cpu(0, rcu_nocb_mask); #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ -#ifdef CONFIG_RCU_NOCB_CPU_ALL - pr_info("\tOffload RCU callbacks from all CPUs\n"); - cpumask_copy(rcu_nocb_mask, cpu_possible_mask); -#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ if (have_rcu_nocb_mask) { if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { -- 1.9.1