sched/fair: introduce minimum capacity capping sched feature

We have the ability to track minimum capacity forced onto a CPU by
userspace or external actors. This is provided though a minimum
frequency scale factor exposed by arch_scale_min_freq_capacity.

The use of this information is enabled through the MIN_CAPACITY_CAPPING
feature. If not enabled, the minimum frequency scale factor will
remain 0 and it will not impact energy estimation or scheduling
decisions.

Change-Id: Ibc61f2bf4fddf186695b72b262e602a6e8bfde37
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

kernel/sched/fair.c

@@ -5424,6 +5424,20 @@ unsigned long capacity_curr_of(int cpu)
 	       >> SCHED_CAPACITY_SHIFT;
 }
 
+/*
+ * Returns the current capacity of cpu after applying both
+ * cpu and min freq scaling.
+ */
+unsigned long capacity_min_of(int cpu)
+{
+	if (!sched_feat(MIN_CAPACITY_CAPPING))
+		return 0;
+	return arch_scale_cpu_capacity(NULL, cpu) *
+	       arch_scale_min_freq_capacity(NULL, cpu)
+	       >> SCHED_CAPACITY_SHIFT;
+}
+
+
 static inline bool energy_aware(void)
 {
 	return sched_feat(ENERGY_AWARE);

kernel/sched/features.h

@@ -78,3 +78,11 @@ SCHED_FEAT(ENERGY_AWARE, true)
 #else
 SCHED_FEAT(ENERGY_AWARE, false)
 #endif
+
+/*
+ * Minimum capacity capping. Keep track of minimum capacity factor when
+ * minimum frequency available to a policy is modified.
+ * If enabled, this can be used to inform the scheduler about capacity
+ * restrictions.
+ */
+SCHED_FEAT(MIN_CAPACITY_CAPPING, false)