Messages in this thread | | | Date | Fri, 9 Aug 2013 17:44:56 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH RFC nohz_full 4/7] nohz_full: Add full-system idle states and variables |
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On Fri, Jul 26, 2013 at 04:19:21PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > 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 <paulmck@linux.vnet.ibm.com> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > --- > 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 >
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