From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934011AbbELVrR (ORCPT ); Tue, 12 May 2015 17:47:17 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:58177 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754075AbbELVp7 (ORCPT ); Tue, 12 May 2015 17:45:59 -0400 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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/15] rcu: Force wakeup of rcu_gp_kthread at grace-period end Date: Tue, 12 May 2015 14:38:13 -0700 Message-Id: <1431466701-653-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1431466701-653-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20150512213756.GA32729@linux.vnet.ibm.com> <1431466701-653-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15051221-0009-0000-0000-00000AC69A80 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" The rcu_gp_kthread_wake() refuses to do a wakeup unless at least one of the ->gp_flags bits are set, which normally will not be the case when the last quiescent state is reported. This results in up to a 3-jiffy delay given default Kconfig settings. This commit therefore has rcu_report_qs_rsp() set RCU_GP_FLAG_FQS before invoking rcu_gp_kthread_wake() in order to force a more immediate wakeup at grace-period end, thus reducing grace-period latencies. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 04bca6b1b9ca..a7615a0b684f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2137,6 +2137,7 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); + WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); rcu_gp_kthread_wake(rsp); } -- 1.8.1.5