On Sat, Aug 17, 2013 at 06:49:41PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul...@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 <paul...@linux.vnet.ibm.com> > Cc: Frederic Weisbecker <fweis...@gmail.com> > Cc: Steven Rostedt <rost...@goodmis.org>
One issue (and one question) below; with the issue addressed, Reviewed-by: Josh Triplett <j...@joshtriplett.org> > kernel/rcutree_plugin.h | 28 ++++++++++++++++++++++++++++ > 1 file changed, 28 insertions(+) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index eab81da..64a05b9f 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -2378,6 +2378,34 @@ 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 I don't see any Kconfig creating this new config option. Also, why not simply define this config option unconditionally, with a default of 8, and then use its value directly? > +static int __maybe_unused full_sysidle_state; /* Current system-idle state. > */ > +#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. */ Perhaps there's a kernel style rule I'm not thinking of that makes it verboten, but: why not use an enum for a state variable like this? - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
