s390/hiperdispatch: Add steal time averaging

The measurements done by hiperdispatch can have sudden spikes and dips
during run time. To prevent these outliers effecting the decision making
process and causing adjustment overhead, use weighted average of the
steal time.

Acked-by: Vasily Gorbik <[email protected]>
Co-developed-by: Tobias Huschle <[email protected]>
Signed-off-by: Tobias Huschle <[email protected]>
Signed-off-by: Mete Durlu <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>

Author: NickJackolson

arch/s390/kernel/hiperdispatch.c

@@ -56,6 +56,7 @@
 #define HD_DELAY_FACTOR			(4)
 #define HD_DELAY_INTERVAL		(HZ / 4)
 #define HD_STEAL_THRESHOLD		30
+#define HD_STEAL_AVG_WEIGHT		16
 
 static cpumask_t hd_vl_coremask;	/* Mask containing all vertical low COREs */
 static cpumask_t hd_vmvl_cpumask;	/* Mask containing vertical medium and low CPUs */
@@ -136,6 +137,14 @@ int hd_enable_hiperdispatch(void)
 	return 1;
 }
 
+static unsigned long hd_steal_avg(unsigned long new)
+{
+	static unsigned long steal;
+
+	steal = (steal * (HD_STEAL_AVG_WEIGHT - 1) + new) / HD_STEAL_AVG_WEIGHT;
+	return steal;
+}
+
 static unsigned long hd_calculate_steal_percentage(void)
 {
 	unsigned long time_delta, steal_delta, steal, percentage;
@@ -185,7 +194,7 @@ static void hd_capacity_work_fn(struct work_struct *work)
 		mutex_unlock(&smp_cpu_state_mutex);
 		return;
 	}
-	steal_percentage = hd_calculate_steal_percentage();
+	steal_percentage = hd_steal_avg(hd_calculate_steal_percentage());
 	if (steal_percentage < HD_STEAL_THRESHOLD)
 		new_cores = hd_online_cores;
 	else