[RFT][PATCH v2 2/3] cpuidle: teo: Skip tick_nohz_get_sleep_length() call in some cases

Rafael J. Wysocki
2023-08-03T21:12:00Z

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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>
---

v1 -> v2: No changes

---
drivers/cpuidle/governors/teo.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

Index: linux-pm/drivers/cpuidle/governors/teo.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/teo.c
+++ linux-pm/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_dri
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;