[v8,03/10] sched: idle: Do not stop the tick before cpuidle_idle_call()

Commit Message

Rafael J. Wysocki March 29, 2018, 12:02 p.m. UTC

From: Rafael J. Wysocki <[e-mail]>

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 <[e-mail]>
---

v7 -> v8: No changes.

---
 kernel/sched/idle.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

Comments

Frederic Weisbecker April 2, 2018, 9:25 p.m. UTC | #1

On Thu, Mar 29, 2018 at 02:02:24PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <[e-mail]>
> 
> 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 <[e-mail]>

Rewiewed-by: Frederic Weisbecker <[e-mail]>

Patch

Index: linux-pm/kernel/sched/idle.c
===================================================================
--- linux-pm.orig/kernel/sched/idle.c
+++ linux-pm/kernel/sched/idle.c
@@ -146,13 +146,15 @@  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;
 	}
@@ -169,16 +171,26 @@  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.
 		 */
@@ -245,7 +257,6 @@  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();