nohz: Remove tick_nohz_idle_enter_norcu() / tick_nohz_idle_exit_norcu()

Those two APIs were provided to optimize the calls of
tick_nohz_idle_enter() and rcu_idle_enter() into a single
irq disabled section. This way no interrupt happening in-between would
needlessly process any RCU job.

Now we are talking about an optimization for which benefits
have yet to be measured. Let's start simple and completely decouple
idle rcu and dyntick idle logics to simplify.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c76aefe764b0..0ec8b832ab6b 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -454,21 +454,20 @@ out:
  * When the next event is more than a tick into the future, stop the idle tick
  * Called when we start the idle loop.
  *
- * If no use of RCU is made in the idle loop between
- * tick_nohz_idle_enter() and tick_nohz_idle_exit() calls, then
- * tick_nohz_idle_enter_norcu() should be called instead and the arch
- * doesn't need to call rcu_idle_enter() and rcu_idle_exit() explicitly.
- *
- * Otherwise the arch is responsible of calling:
+ * The arch is responsible of calling:
  *
  * - rcu_idle_enter() after its last use of RCU before the CPU is put
  *  to sleep.
  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
  */
-void __tick_nohz_idle_enter(void)
+void tick_nohz_idle_enter(void)
 {
         struct tick_sched *ts;
 
+        WARN_ON_ONCE(irqs_disabled());
+
+        local_irq_disable();
+
         ts = &__get_cpu_var(tick_cpu_sched);
         /*
          * set ts->inidle unconditionally. even if the system did not
@@ -477,6 +476,8 @@ void __tick_nohz_idle_enter(void)
          */
         ts->inidle = 1;
         tick_nohz_stop_sched_tick(ts);
+
+        local_irq_enable();
 }
 
 /**