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>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f3de37414a664e69f3ab61003676ff27289f011c..043715612227333c3b1486e729339693c84da36b 100644 (file)
--- 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