Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932210AbaGSQx6 (ORCPT ); Sat, 19 Jul 2014 12:53:58 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:38075 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932075AbaGSQx4 (ORCPT ); Sat, 19 Jul 2014 12:53:56 -0400 Date: Sat, 19 Jul 2014 09:53:50 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: [PATCH tip/core/rcu] Do not keep timekeeping CPU tick running for non-nohz_full= CPUs Message-ID: <20140719165350.GA18411@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14071916-1542-0000-0000-00000367A2AB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If a non-nohz_full= CPU is non-idle, it will have a scheduling-clock interrupt, and therefore doesn't need the timekeeping CPU to keep its scheduling-clock interrupt going. This commit therefore ignores the idle state of non-nohz_full CPUs when determining whether or not the timekeeping CPU can safely turn off its scheduling-clock interrupt. Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index ddad959a9132..eaa32e4c228d 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2789,8 +2789,13 @@ static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) * system-idle state. This means that the timekeeping CPU must * invoke rcu_sysidle_force_exit() directly if it does anything * more than take a scheduling-clock interrupt. + * + * In addition if we are not a nohz_full= CPU, then when we are + * non-idle we have our own tick, so we don't need the timekeeping + * CPU to keep a tick on our behalf. We assume that the timekeeping + * CPU is also a nohz_full= CPU. */ - if (smp_processor_id() == tick_do_timer_cpu) + if (!tick_nohz_full_cpu(smp_processor_id())) return; /* Update system-idle state: We are clearly no longer fully idle! */ @@ -2810,11 +2815,11 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, /* * If some other CPU has already reported non-idle, if this is - * not the flavor of RCU that tracks sysidle state, or if this - * is an offline or the timekeeping CPU, nothing to do. + * not the flavor of RCU that tracks sysidle state, or if this is + * an offline or !nohz_full= or the timekeeping CPU, nothing to do. */ if (!*isidle || rdp->rsp != rcu_sysidle_state || - cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) + cpu_is_offline(rdp->cpu) || !tick_nohz_full_cpu(rdp->cpu)) return; if (rcu_gp_in_progress(rdp->rsp)) WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/