From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754329AbaH1TUZ (ORCPT ); Thu, 28 Aug 2014 15:20:25 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:32786 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752927AbaH1TUS (ORCPT ); Thu, 28 Aug 2014 15:20:18 -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 v7 tip/core/rcu 09/17] rcu: Improve RCU-tasks energy efficiency Date: Thu, 28 Aug 2014 12:20:00 -0700 Message-Id: <1409253608-32538-9-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1409253608-32538-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20140828191929.GA31795@linux.vnet.ibm.com> <1409253608-32538-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14082819-6688-0000-0000-0000045BBBB8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" The current RCU-tasks implementation uses strict polling to detect callback arrivals. This works quite well, but is not so good for energy efficiency. This commit therefore replaces the strict polling with a wait queue. Signed-off-by: Paul E. McKenney --- kernel/rcu/update.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index bad7dbd4c2e3..444c8a303963 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -365,6 +365,7 @@ early_initcall(check_cpu_stall_init); /* Global list of callbacks and associated lock. */ static struct rcu_head *rcu_tasks_cbs_head; static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; +static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq); static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); /* Track exiting tasks in order to allow them to be waited for. */ @@ -378,13 +379,17 @@ module_param(rcu_task_stall_timeout, int, 0644); void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp)) { unsigned long flags; + bool needwake; rhp->next = NULL; rhp->func = func; raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); + needwake = !rcu_tasks_cbs_head; *rcu_tasks_cbs_tail = rhp; rcu_tasks_cbs_tail = &rhp->next; raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); + if (needwake) + wake_up(&rcu_tasks_cbs_wq); } EXPORT_SYMBOL_GPL(call_rcu_tasks); @@ -495,8 +500,12 @@ static int __noreturn rcu_tasks_kthread(void *arg) /* If there were none, wait a bit and start over. */ if (!list) { - schedule_timeout_interruptible(HZ); - WARN_ON(signal_pending(current)); + wait_event_interruptible(rcu_tasks_cbs_wq, + rcu_tasks_cbs_head); + if (!rcu_tasks_cbs_head) { + WARN_ON(signal_pending(current)); + schedule_timeout_interruptible(HZ/10); + } continue; } @@ -602,6 +611,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) list = next; cond_resched(); } + schedule_timeout_uninterruptible(HZ/10); } } -- 1.8.1.5