Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967998Ab3HIPpB (ORCPT ); Fri, 9 Aug 2013 11:45:01 -0400 Received: from mail-we0-f173.google.com ([74.125.82.173]:63803 "EHLO mail-we0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967927Ab3HIPpA (ORCPT ); Fri, 9 Aug 2013 11:45:00 -0400 Date: Fri, 9 Aug 2013 17:44:56 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, sbw@mit.edu Subject: Re: [PATCH RFC nohz_full 4/7] nohz_full: Add full-system idle states and variables Message-ID: <20130809154454.GB13339@somewhere> References: <20130726231848.GA12967@linux.vnet.ibm.com> <1374880764-14248-1-git-send-email-paulmck@linux.vnet.ibm.com> <1374880764-14248-4-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: <1374880764-14248-4-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 Content-Length: 3423 Lines: 83 On Fri, Jul 26, 2013 at 04:19:21PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > This commit adds control variables and states for full-system idle. > The system will progress through the states in numerical order when > the system is fully idle (other than the timekeeping CPU), and reset > down to the initial state if any non-timekeeping CPU goes non-idle. > The current state is kept in full_sysidle_state. > > A RCU_SYSIDLE_SMALL macro is defined, and systems with this number > of CPUs or fewer move through the states more aggressively. The idea > is that the resulting memory contention is less of a problem on small > systems. Architectures can adjust this value (which defaults to 8) > using CONFIG_ARCH_RCU_SYSIDLE_SMALL. > > One flavor of RCU will be in charge of driving the state machine, > defined by rcu_sysidle_state. This should be the busiest flavor of RCU. > > Signed-off-by: Paul E. McKenney > Cc: Frederic Weisbecker > Cc: Steven Rostedt > --- > kernel/rcutree_plugin.h | 28 ++++++++++++++++++++++++++++ > 1 file changed, 28 insertions(+) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 814ff47..3edae39 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -2380,6 +2380,34 @@ static void rcu_kick_nohz_cpu(int cpu) > #ifdef CONFIG_NO_HZ_FULL_SYSIDLE > > /* > + * Handle small systems specially, accelerating their transition into > + * full idle state. Allow arches to override this code's idea of > + * what constitutes a "small" system. > + */ > +#ifdef CONFIG_ARCH_RCU_SYSIDLE_SMALL > +#define RCU_SYSIDLE_SMALL CONFIG_ARCH_RCU_SYSIDLE_SMALL > +#else /* #ifdef CONFIG_ARCH_RCU_SYSIDLE_SMALL */ > +#define RCU_SYSIDLE_SMALL 8 > +#endif > + > +/* > + * Define RCU flavor that holds sysidle state. This needs to be the > + * most active flavor of RCU. > + */ > +#ifdef CONFIG_PREEMPT_RCU > +static struct rcu_state __maybe_unused *rcu_sysidle_state = &rcu_preempt_state; > +#else /* #ifdef CONFIG_PREEMPT_RCU */ > +static struct rcu_state __maybe_unused *rcu_sysidle_state = &rcu_sched_state; > +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ Why the maybe_unused here? Couldn't we get rid of it if those definitions were under NO_HZ_FULL_SYSIDLE? > + > +static int __maybe_unused full_sysidle_state; /* Current system-idle state. */ Ditto here? > +#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ > +#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ > +#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ > +#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ > +#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ This may be better as an enum. This way the variables that store such values can carry this type and the review becomes easier. > + > +/* > * Invoked to note exit from irq or task transition to idle. Note that > * usermode execution does -not- count as idle here! After all, we want > * to detect full-system idle states, not RCU quiescent states and grace > -- > 1.8.1.5 > -- 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/