cpuidle: menu: Avoid computations when result will be discarded

If the minimum interval taken into account in the average computation
loop in get_typical_interval() is less than the expected idle
duration determined so far, the resultant average cannot be greater
than that value as well and the entire return result of the function
is going to be discarded anyway going forward.

In that case, it is a waste of time to carry out the remaining
computations in get_typical_interval(), so avoid that by returning
early if the minimum interval is not below the expected idle duration.

No intentional changes of behavior.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 3d283211ad774cc1bc9464a3dcf0755b1f106eaa..575a68f31761f92b4e5cec1ca956628e750c6a47 100644 (file)
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -196,10 +196,11 @@ static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev);
  * of points is below a threshold. If it is... then use the
  * average of these 8 points as the estimated value.
  */
-static unsigned int get_typical_interval(struct menu_device *data)
+static unsigned int get_typical_interval(struct menu_device *data,
+                                        unsigned int predicted_us)
 {
        int i, divisor;
-       unsigned int max, thresh, avg;
+       unsigned int min, max, thresh, avg;
        uint64_t sum, variance;
 
        thresh = UINT_MAX; /* Discard outliers above this value */
@@ -207,6 +208,7 @@ static unsigned int get_typical_interval(struct menu_device *data)
 again:
 
        /* First calculate the average of past intervals */
+       min = UINT_MAX;
        max = 0;
        sum = 0;
        divisor = 0;
@@ -217,8 +219,19 @@ static unsigned int get_typical_interval(struct menu_device *data)
                        divisor++;
                        if (value > max)
                                max = value;
+
+                       if (value < min)
+                               min = value;
                }
        }
+
+       /*
+        * If the result of the computation is going to be discarded anyway,
+        * avoid the computation altogether.
+        */
+       if (min >= predicted_us)
+               return UINT_MAX;
+
        if (divisor == INTERVALS)
                avg = sum >> INTERVAL_SHIFT;
        else
@@ -325,7 +338,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
        /*
         * Use the lowest expected idle interval to pick the idle state.
         */
-       predicted_us = min(predicted_us, get_typical_interval(data));
+       predicted_us = min(predicted_us, get_typical_interval(data, predicted_us));
 
        if (tick_nohz_tick_stopped()) {
                /*