cpuidle: menu: help gcc generate slightly better code

We know that the avg variable actually ends up holding a 32 bit
quantity, since it's an average of such numbers. It is only a u64
because it is temporarily used to hold the sum. Making it an actual
u32 allows gcc to generate slightly better code, e.g. when computing
the square, it can do a 32x32->64 multiply.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
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 beef7ae..27fc733 100644 (file)
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -199,8 +199,8 @@ static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev);
 static void get_typical_interval(struct menu_device *data)
 {
        int i, divisor;
-       unsigned int max, thresh;
-       uint64_t avg, variance;
+       unsigned int max, thresh, avg;
+       uint64_t sum, variance;
 
        thresh = UINT_MAX; /* Discard outliers above this value */
 
@@ -208,28 +208,28 @@ again:
 
        /* First calculate the average of past intervals */
        max = 0;
-       avg = 0;
+       sum = 0;
        divisor = 0;
        for (i = 0; i < INTERVALS; i++) {
                unsigned int value = data->intervals[i];
                if (value <= thresh) {
-                       avg += value;
+                       sum += value;
                        divisor++;
                        if (value > max)
                                max = value;
                }
        }
        if (divisor == INTERVALS)
-               avg >>= INTERVAL_SHIFT;
+               avg = sum >> INTERVAL_SHIFT;
        else
-               do_div(avg, divisor);
+               avg = div_u64(sum, divisor);
 
        /* Then try to determine variance */
        variance = 0;
        for (i = 0; i < INTERVALS; i++) {
                unsigned int value = data->intervals[i];
                if (value <= thresh) {
-                       int64_t diff = value - avg;
+                       int64_t diff = (int64_t)value - avg;
                        variance += diff * diff;
                }
        }
@@ -251,7 +251,7 @@ again:
         * Use this result only if there is no timer to wake us up sooner.
         */
        if (likely(variance <= U64_MAX/36)) {
-               if (((avg*avg > variance*36) && (divisor * 4 >= INTERVALS * 3))
+               if ((((u64)avg*avg > variance*36) && (divisor * 4 >= INTERVALS * 3))
                                                        || variance <= 400) {
                        if (data->next_timer_us > avg)
                                data->predicted_us = avg;