sched: Estimate energy impact of scheduling decisions

Adds a generic energy-aware helper function, energy_diff(), that
calculates energy impact of adding, removing, and migrating utilization
in the system.

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

1 files changed, 52 insertions, 0 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f3de37414a66..043715612227 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4893,6 +4893,58 @@ next_cpu:
 	return 0;
 }
 
+static inline bool cpu_in_sg(struct sched_group *sg, int cpu)
+{
+	return cpu != -1 && cpumask_test_cpu(cpu, sched_group_cpus(sg));
+}
+
+/*
+ * energy_diff(): Estimate the energy impact of changing the utilization
+ * distribution. eenv specifies the change: utilisation amount, source, and
+ * destination cpu. Source or destination cpu may be -1 in which case the
+ * utilization is removed from or added to the system (e.g. task wake-up). If
+ * both are specified, the utilization is migrated.
+ */
+static int energy_diff(struct energy_env *eenv)
+{
+	struct sched_domain *sd;
+	struct sched_group *sg;
+	int sd_cpu = -1, energy_before = 0, energy_after = 0;
+
+	struct energy_env eenv_before = {
+		.util_delta	= 0,
+		.src_cpu	= eenv->src_cpu,
+		.dst_cpu	= eenv->dst_cpu,
+	};
+
+	if (eenv->src_cpu == eenv->dst_cpu)
+		return 0;
+
+	sd_cpu = (eenv->src_cpu != -1) ? eenv->src_cpu : eenv->dst_cpu;
+	sd = rcu_dereference(per_cpu(sd_ea, sd_cpu));
+
+	if (!sd)
+		return 0; /* Error */
+
+	sg = sd->groups;
+
+	do {
+		if (cpu_in_sg(sg, eenv->src_cpu) || cpu_in_sg(sg, eenv->dst_cpu)) {
+			eenv_before.sg_top = eenv->sg_top = sg;
+
+			if (sched_group_energy(&eenv_before))
+				return 0; /* Invalid result abort */
+			energy_before += eenv_before.energy;
+
+			if (sched_group_energy(eenv))
+				return 0; /* Invalid result abort */
+			energy_after += eenv->energy;
+		}
+	} while (sg = sg->next, sg != sd->groups);
+
+	return energy_after-energy_before;
+}
+
 /*
  * 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