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>

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 3d84dbc..42ca5a4 100644 (file)
--- 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();