cpuidle: menu: Refine idle state selection for running tick

If the tick isn't stopped, the target residency of the state selected
by the menu governor may be greater than the actual time to the next
tick and that means lost energy.

To avoid that, make tick_nohz_get_sleep_length() return the current
time to the next event (before stopping the tick) in addition to the
estimated one via an extra pointer argument and make menu_select()
use that value to refine the state selection when necessary.

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

1 files changed, 25 insertions, 2 deletions

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index f53a929bd2bd..267982e471e0 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -295,6 +295,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 	unsigned int expected_interval;
 	unsigned long nr_iowaiters, cpu_load;
 	int resume_latency = dev_pm_qos_raw_read_value(device);
+	ktime_t delta_next;
 
 	if (data->needs_update) {
 		menu_update(drv, dev);
@@ -312,7 +313,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 	}
 
 	/* determine the expected residency time, round up */
-	data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length());
+	data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length(&delta_next));
 
 	get_iowait_load(&nr_iowaiters, &cpu_load);
 	data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
@@ -396,9 +397,31 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 	 * expected idle duration is shorter than the tick period length.
 	 */
 	if ((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
-	    expected_interval < TICK_USEC)
+	    expected_interval < TICK_USEC) {
+		unsigned int delta_next_us = ktime_to_us(delta_next);
+
 		*stop_tick = false;
 
+		if (!tick_nohz_tick_stopped() && idx > 0 &&
+		    drv->states[idx].target_residency > delta_next_us) {
+			/*
+			 * The tick is not going to be stopped and the target
+			 * residency of the state to be returned is not within
+			 * the time until the next timer event including the
+			 * tick, so try to correct that.
+			 */
+			for (i = idx - 1; i >= 0; i--) {
+			    if (drv->states[i].disabled ||
+			        dev->states_usage[i].disable)
+					continue;
+
+				idx = i;
+				if (drv->states[i].target_residency <= delta_next_us)
+					break;
+			}
+		}
+	}
+
 	data->last_state_idx = idx;
 
 	return data->last_state_idx;