rcu: Reduce latency of rcu_prepare_for_idle()

Re-enable interrupts across calls to quiescent-state functions and
also across force_quiescent_state() to reduce latency.

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

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 3d84dbc113d6..42ca5a400ae3 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2009,7 +2009,6 @@ int rcu_needs_cpu(int cpu)
  */
 static void rcu_prepare_for_idle(int cpu)
 {
-        int c = 0;
         unsigned long flags;
 
         local_irq_save(flags);
@@ -2055,27 +2054,30 @@ static void rcu_prepare_for_idle(int cpu)
          */
 #ifdef CONFIG_TREE_PREEMPT_RCU
         if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
+                local_irq_restore(flags);
                 rcu_preempt_qs(cpu);
                 force_quiescent_state(&rcu_preempt_state, 0);
-                c = c || per_cpu(rcu_preempt_data, cpu).nxtlist;
+                local_irq_save(flags);
         }
 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
         if (per_cpu(rcu_sched_data, cpu).nxtlist) {
+                local_irq_restore(flags);
                 rcu_sched_qs(cpu);
                 force_quiescent_state(&rcu_sched_state, 0);
-                c = c || per_cpu(rcu_sched_data, cpu).nxtlist;
+                local_irq_save(flags);
         }
         if (per_cpu(rcu_bh_data, cpu).nxtlist) {
+                local_irq_restore(flags);
                 rcu_bh_qs(cpu);
                 force_quiescent_state(&rcu_bh_state, 0);
-                c = c || per_cpu(rcu_bh_data, cpu).nxtlist;
+                local_irq_save(flags);
         }
 
         /*
          * If RCU callbacks are still pending, RCU still needs this CPU.
          * So try forcing the callbacks through the grace period.
          */
-        if (c) {
+        if (rcu_cpu_has_callbacks(cpu)) {
                 local_irq_restore(flags);
                 trace_rcu_prep_idle("More callbacks");
                 invoke_rcu_core();