cpuidle: teo: Skip tick_nohz_get_sleep_length() call in some cases

Make teo_select() avoid calling tick_nohz_get_sleep_length() if the
candidate idle state to return is state 0 or if state 0 is a polling
one and the target residency of the current candidate one is below
a certain threshold, in which cases it may be assumed that the CPU will
be woken up immediately by a non-timer wakeup source and the timers
are not likely to matter.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
Tested-by: Anna-Maria Behnsen <anna-maria@linutronix.de>

diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
index 4ef76cd..8248492 100644 (file)
--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -166,6 +166,12 @@
  */
 #define NR_RECENT      9
 
+/*
+ * Idle state target residency threshold used for deciding whether or not to
+ * check the time till the closest expected timer event.
+ */
+#define RESIDENCY_THRESHOLD_NS (15 * NSEC_PER_USEC)
+
 /**
  * struct teo_bin - Metrics used by the TEO cpuidle governor.
  * @intercepts: The "intercepts" metric.
@@ -542,6 +548,22 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
                        idx = i;
        }
 
+       /*
+        * Skip the timers check if state 0 is the current candidate one,
+        * because an immediate non-timer wakeup is expected in that case.
+        */
+       if (!idx)
+               goto out_tick;
+
+       /*
+        * If state 0 is a polling one, check if the target residency of
+        * the current candidate state is low enough and skip the timers
+        * check in that case too.
+        */
+       if ((drv->states[0].flags & CPUIDLE_FLAG_POLLING) &&
+           drv->states[idx].target_residency_ns < RESIDENCY_THRESHOLD_NS)
+               goto out_tick;
+
        duration_ns = tick_nohz_get_sleep_length(&delta_tick);
        cpu_data->sleep_length_ns = duration_ns;