sched: idle: Do not stop the tick before cpuidle_idle_call()

Make cpuidle_idle_call() decide whether or not to stop the tick.

First, the cpuidle_enter_s2idle() path deals with the tick (and with
the entire timekeeping for that matter) by itself and it doesn't need
the tick to be stopped beforehand.

Second, to address the issue with short idle duration predictions
by the idle governor after the tick has been stopped, it will be
necessary to change the ordering of cpuidle_select() with respect
to tick_nohz_idle_stop_tick().  To prepare for that, put a
tick_nohz_idle_stop_tick() call in the same branch in which
cpuidle_select() is called.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 3777e83c0b5aea7f85972d7fcc09da53261892e2..4f64835d38a847ca0c57d9e5c09e182246eb2ecd 100644 (file)
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -141,13 +141,15 @@ static void cpuidle_idle_call(void)
        }
 
        /*
-        * Tell the RCU framework we are entering an idle section,
-        * so no more rcu read side critical sections and one more
+        * The RCU framework needs to be told that we are entering an idle
+        * section, so no more rcu read side critical sections and one more
         * step to the grace period
         */
-       rcu_idle_enter();
 
        if (cpuidle_not_available(drv, dev)) {
+               tick_nohz_idle_stop_tick();
+               rcu_idle_enter();
+
                default_idle_call();
                goto exit_idle;
        }
@@ -164,16 +166,26 @@ static void cpuidle_idle_call(void)
 
        if (idle_should_enter_s2idle() || dev->use_deepest_state) {
                if (idle_should_enter_s2idle()) {
+                       rcu_idle_enter();
+
                        entered_state = cpuidle_enter_s2idle(drv, dev);
                        if (entered_state > 0) {
                                local_irq_enable();
                                goto exit_idle;
                        }
+
+                       rcu_idle_exit();
                }
 
+               tick_nohz_idle_stop_tick();
+               rcu_idle_enter();
+
                next_state = cpuidle_find_deepest_state(drv, dev);
                call_cpuidle(drv, dev, next_state);
        } else {
+               tick_nohz_idle_stop_tick();
+               rcu_idle_enter();
+
                /*
                 * Ask the cpuidle framework to choose a convenient idle state.
                 */
@@ -240,7 +252,6 @@ static void do_idle(void)
                        tick_nohz_idle_restart_tick();
                        cpu_idle_poll();
                } else {
-                       tick_nohz_idle_stop_tick();
                        cpuidle_idle_call();
                }
                arch_cpu_idle_exit();