[PATCH 5/6] cpuidle: menu: Avoid computations for very close timers

Rafael J. Wysocki
2018-10-02T21:46:28Z

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

If the next timer event (with the tick excluded) is closer than the
target residency of the second state or the PM QoS latency constraint
is below its exit latency, state[0] will be used regardless of any
other factors, so skip the computations in menu_select() then and
return 0 straight away from it.

Still, do that after the bucket has been determined to avoid
disturbing the wakeup statistics in general.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpuidle/governors/menu.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

Index: linux-pm/drivers/cpuidle/governors/menu.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/menu.c
+++ linux-pm/drivers/cpuidle/governors/menu.c
@@ -309,6 +309,18 @@ static int menu_select(struct cpuidle_dr
get_iowait_load(&nr_iowaiters, &cpu_load);
data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);

+ if (unlikely(drv->state_count <= 1) ||
+ ((data->next_timer_us < drv->states[1].target_residency ||
+ latency_req < drv->states[1].exit_latency) &&
+ !drv->states[0].disabled && !dev->states_usage[0].disable)) {
+ /*
+ * In this case state[0] will be used no matter what, so return
+ * it right away and keep the tick running.
+ */
+ *stop_tick = false;
+ return 0;
+ }
+
/*
* Force the result of multiplication to be 64 bits even if both
* operands are 32 bits.