From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752487AbaAOUeH (ORCPT ); Wed, 15 Jan 2014 15:34:07 -0500 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:55312 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752452AbaAOUeE (ORCPT ); Wed, 15 Jan 2014 15:34:04 -0500 X-Originating-IP: 173.246.103.110 Date: Wed, 15 Jan 2014 12:33:55 -0800 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu Subject: Re: [PATCH tip/core/timers 2/4] timers: Reduce __run_timers() latency for empty list Message-ID: <20140115203354.GC11147@jtriplet-mobl1> References: <20140115051939.GA31164@linux.vnet.ibm.com> <1389763248-31297-1-git-send-email-paulmck@linux.vnet.ibm.com> <1389763248-31297-2-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389763248-31297-2-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 14, 2014 at 09:20:46PM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > The __run_timers() function currently steps through the list one jiffy at > a time in order to update the timer wheel. However, if the timer wheel > is empty, no adjustment is needed other than updating ->timer_jiffies. > In this case, which is likely to be common for NO_HZ_FULL kernels, the > kernel currently incurs a large latency for no good reason. This commit > therefore short-circuits this case. > > Signed-off-by: Paul E. McKenney > --- > kernel/timer.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/kernel/timer.c b/kernel/timer.c > index 2245b7374c3d..295837e5e011 100644 > --- a/kernel/timer.c > +++ b/kernel/timer.c > @@ -338,6 +338,17 @@ void set_timer_slack(struct timer_list *timer, int slack_hz) > } > EXPORT_SYMBOL_GPL(set_timer_slack); > > +static bool catchup_timer_jiffies(struct tvec_base *base) > +{ > +#ifdef CONFIG_NO_HZ_FULL > + if (!base->all_timers) { > + base->timer_jiffies = jiffies; > + return 1; > + } > +#endif /* #ifdef CONFIG_NO_HZ_FULL */ > + return 0; > +} In a function with return type "bool", please use true/false, not 1/0. Please also document the semantic of the return value. - Josh Triplett