sched: Calculate energy consumption of sched_group

For energy-aware load-balancing decisions it is necessary to know the
energy consumption estimates of groups of cpus. This patch introduces a
basic function, sched_group_energy(), which estimates the energy
consumption of the cpus in the group and any resources shared by the
members of the group.

NOTE: The function has five levels of identation and breaks the 80
character limit. Refactoring is necessary.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>

kernel/sched/core.c

@@ -5994,6 +5994,7 @@ DEFINE_PER_CPU(struct sched_domain *, sd_numa);
 DEFINE_PER_CPU(struct sched_domain *, sd_busy);
 DEFINE_PER_CPU(struct sched_domain *, sd_asym);
 DEFINE_PER_CPU(struct sched_domain *, sd_ea);
+DEFINE_PER_CPU(struct sched_domain *, sd_scs);
 
 static void update_top_cache_domain(int cpu)
 {
@@ -6027,6 +6028,9 @@ static void update_top_cache_domain(int cpu)
 			break;
 	}
 	rcu_assign_pointer(per_cpu(sd_ea, cpu), ea_sd);
+
+	sd = highest_flag_domain(cpu, SD_SHARE_CAP_STATES);
+	rcu_assign_pointer(per_cpu(sd_scs, cpu), sd);
 }
 
 /*

kernel/sched/fair.c

@@ -4701,6 +4701,162 @@ static inline bool energy_aware(void)
 	return sched_feat(ENERGY_AWARE);
 }
 
+/*
+ * cpu_norm_util() returns the cpu util relative to a specific capacity,
+ * i.e. it's busy ratio, in the range [0..SCHED_LOAD_SCALE] which is useful for
+ * energy calculations. Using the scale-invariant util returned by
+ * cpu_util() and approximating scale-invariant util by:
+ *
+ *   util ~ (curr_freq/max_freq)*1024 * capacity_orig/1024 * running_time/time
+ *
+ * the normalized util can be found using the specific capacity.
+ *
+ *   capacity = capacity_orig * curr_freq/max_freq
+ *
+ *   norm_util = running_time/time ~ util/capacity
+ */
+static unsigned long cpu_norm_util(int cpu, unsigned long capacity)
+{
+	int util = cpu_util(cpu);
+
+	if (util >= capacity)
+		return SCHED_CAPACITY_SCALE;
+
+	return (util << SCHED_CAPACITY_SHIFT)/capacity;
+}
+
+static unsigned long group_max_util(struct sched_group *sg)
+{
+	int i;
+	unsigned long max_util = 0;
+
+	for_each_cpu(i, sched_group_cpus(sg))
+		max_util = max(max_util, cpu_util(i));
+
+	return max_util;
+}
+
+/*
+ * group_norm_util() returns the approximated group util relative to it's
+ * current capacity (busy ratio) in the range [0..SCHED_LOAD_SCALE] for use in
+ * energy calculations. Since task executions may or may not overlap in time in
+ * the group the true normalized util is between max(cpu_norm_util(i)) and
+ * sum(cpu_norm_util(i)) when iterating over all cpus in the group, i. The
+ * latter is used as the estimate as it leads to a more pessimistic energy
+ * estimate (more busy).
+ */
+static unsigned long group_norm_util(struct sched_group *sg, int cap_idx)
+{
+	int i;
+	unsigned long util_sum = 0;
+	unsigned long capacity = sg->sge->cap_states[cap_idx].cap;
+
+	for_each_cpu(i, sched_group_cpus(sg))
+		util_sum += cpu_norm_util(i, capacity);
+
+	if (util_sum > SCHED_CAPACITY_SCALE)
+		return SCHED_CAPACITY_SCALE;
+	return util_sum;
+}
+
+static int find_new_capacity(struct sched_group *sg,
+	const struct sched_group_energy const *sge)
+{
+	int idx;
+	unsigned long util = group_max_util(sg);
+
+	for (idx = 0; idx < sge->nr_cap_states; idx++) {
+		if (sge->cap_states[idx].cap >= util)
+			return idx;
+	}
+
+	return idx;
+}
+
+/*
+ * sched_group_energy(): Computes the absolute energy consumption of cpus
+ * belonging to the sched_group including shared resources shared only by
+ * members of the group. Iterates over all cpus in the hierarchy below the
+ * sched_group starting from the bottom working it's way up before going to
+ * the next cpu until all cpus are covered at all levels. The current
+ * implementation is likely to gather the same util statistics multiple times.
+ * This can probably be done in a faster but more complex way.
+ * Note: sched_group_energy() may fail when racing with sched_domain updates.
+ */
+static int sched_group_energy(struct sched_group *sg_top)
+{
+	struct sched_domain *sd;
+	int cpu, total_energy = 0;
+	struct cpumask visit_cpus;
+	struct sched_group *sg;
+
+	WARN_ON(!sg_top->sge);
+
+	cpumask_copy(&visit_cpus, sched_group_cpus(sg_top));
+
+	while (!cpumask_empty(&visit_cpus)) {
+		struct sched_group *sg_shared_cap = NULL;
+
+		cpu = cpumask_first(&visit_cpus);
+
+		/*
+		 * Is the group utilization affected by cpus outside this
+		 * sched_group?
+		 */
+		sd = rcu_dereference(per_cpu(sd_scs, cpu));
+
+		if (!sd)
+			/*
+			 * We most probably raced with hotplug; returning a
+			 * wrong energy estimation is better than entering an
+			 * infinite loop.
+			 */
+			return -EINVAL;
+
+		if (sd->parent)
+			sg_shared_cap = sd->parent->groups;
+
+		for_each_domain(cpu, sd) {
+			sg = sd->groups;
+
+			/* Has this sched_domain already been visited? */
+			if (sd->child && group_first_cpu(sg) != cpu)
+				break;
+
+			do {
+				struct sched_group *sg_cap_util;
+				unsigned long group_util;
+				int sg_busy_energy, sg_idle_energy, cap_idx;
+
+				if (sg_shared_cap && sg_shared_cap->group_weight >= sg->group_weight)
+					sg_cap_util = sg_shared_cap;
+				else
+					sg_cap_util = sg;
+
+				cap_idx = find_new_capacity(sg_cap_util, sg->sge);
+				group_util = group_norm_util(sg, cap_idx);
+				sg_busy_energy = (group_util * sg->sge->cap_states[cap_idx].power)
+										>> SCHED_CAPACITY_SHIFT;
+				sg_idle_energy = ((SCHED_LOAD_SCALE-group_util) * sg->sge->idle_states[0].power)
+										>> SCHED_CAPACITY_SHIFT;
+
+				total_energy += sg_busy_energy + sg_idle_energy;
+
+				if (!sd->child)
+					cpumask_xor(&visit_cpus, &visit_cpus, sched_group_cpus(sg));
+
+				if (cpumask_equal(sched_group_cpus(sg), sched_group_cpus(sg_top)))
+					goto next_cpu;
+
+			} while (sg = sg->next, sg != sd->groups);
+		}
+next_cpu:
+		continue;
+	}
+
+	return total_energy;
+}
+
 /*
  * Detect M:N waker/wakee relationships via a switching-frequency heuristic.
  * A waker of many should wake a different task than the one last awakened

kernel/sched/sched.h

@@ -840,6 +840,7 @@ DECLARE_PER_CPU(struct sched_domain *, sd_numa);
 DECLARE_PER_CPU(struct sched_domain *, sd_busy);
 DECLARE_PER_CPU(struct sched_domain *, sd_asym);
 DECLARE_PER_CPU(struct sched_domain *, sd_ea);
+DECLARE_PER_CPU(struct sched_domain *, sd_scs);
 
 struct sched_group_capacity {
 	atomic_t ref;