rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks

Because RCU callbacks are now associated with the number of the grace
period that they must wait for, CPUs can now take advance callbacks
corresponding to grace periods that ended while a given CPU was in
dyntick-idle mode.  This eliminates the need to try forcing the RCU
state machine while entering idle, thus reducing the CPU intensiveness
of RCU_FAST_NO_HZ, which should increase its energy efficiency.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 3 insertions, 9 deletions

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index b6c2335efbdf..96a27f922e92 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -88,18 +88,13 @@ struct rcu_dynticks {
         int dynticks_nmi_nesting;   /* Track NMI nesting level. */
         atomic_t dynticks;          /* Even value for idle, else odd. */
 #ifdef CONFIG_RCU_FAST_NO_HZ
-        int dyntick_drain;          /* Prepare-for-idle state variable. */
-        unsigned long dyntick_holdoff;
-                                    /* No retries for the jiffy of failure. */
-        struct timer_list idle_gp_timer;
-                                    /* Wake up CPU sleeping with callbacks. */
-        unsigned long idle_gp_timer_expires;
-                                    /* When to wake up CPU (for repost). */
-        bool idle_first_pass;       /* First pass of attempt to go idle? */
+        bool all_lazy;              /* Are all CPU's CBs lazy? */
         unsigned long nonlazy_posted;
                                     /* # times non-lazy CBs posted to CPU. */
         unsigned long nonlazy_posted_snap;
                                     /* idle-period nonlazy_posted snapshot. */
+        unsigned long last_accelerate;
+                                    /* Last jiffy CBs were accelerated. */
         int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */
 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
 };
@@ -521,7 +516,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
                                                  struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_RCU_BOOST */
 static void __cpuinit rcu_prepare_kthreads(int cpu);
-static void rcu_prepare_for_idle_init(int cpu);
 static void rcu_cleanup_after_idle(int cpu);
 static void rcu_prepare_for_idle(int cpu);
 static void rcu_idle_count_callbacks_posted(void);