From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751554AbaFMARH (ORCPT ); Thu, 12 Jun 2014 20:17:07 -0400 Received: from mail-we0-f181.google.com ([74.125.82.181]:60361 "EHLO mail-we0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056AbaFMARF (ORCPT ); Thu, 12 Jun 2014 20:17:05 -0400 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: LKML , Frederic Weisbecker , Josh Triplett , Steven Rostedt , Mathieu Desnoyers Subject: [PATCH] rcu: Only pin GP kthread when full dynticks is actually used Date: Fri, 13 Jun 2014 02:16:59 +0200 Message-Id: <1402618619-32630-1-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org CONFIG_NO_HZ_FULL may be enabled widely on distros nowadays but actual users should be a tiny minority, if actually any. Also there is a risk that affining the GP kthread to a single CPU could end up noticeably reducing RCU performances and increasing energy consumption. So lets affine the GP kthread only when nohz full is actually used (ie: when the nohz_full= parameter is filled or CONFIG_NO_HZ_FULL_ALL=y) Signed-off-by: Frederic Weisbecker Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers --- kernel/rcu/tree_plugin.h | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index cbc2c45..726f52c 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2843,12 +2843,16 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp) */ static void rcu_bind_gp_kthread(void) { -#ifdef CONFIG_NO_HZ_FULL - int cpu = ACCESS_ONCE(tick_do_timer_cpu); + int cpu; + + if (!tick_nohz_full_enabled()) + return; + + cpu = ACCESS_ONCE(tick_do_timer_cpu); if (cpu < 0 || cpu >= nr_cpu_ids) return; + if (raw_smp_processor_id() != cpu) set_cpus_allowed_ptr(current, cpumask_of(cpu)); -#endif /* #ifdef CONFIG_NO_HZ_FULL */ } -- 1.8.3.1