[RFCv5 PATCH 24/46] sched: Estimate energy impact of scheduling decisions

Morten Rasmussen
2015-07-07T19:00:12Z

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>
---
kernel/sched/fair.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 362e33b..bf1d34c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5026,6 +5026,57 @@ static unsigned int sched_group_energy(struct energy_env *eenv)
return total_energy;
}

+/*
+ * 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 = {
+ .usage_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 (eenv->src_cpu != -1 && cpumask_test_cpu(eenv->src_cpu,
+ sched_group_cpus(sg))) {
+ eenv_before.sg_top = eenv->sg_top = sg;
+ energy_before += sched_group_energy(&eenv_before);
+ energy_after += sched_group_energy(eenv);
+
+ /* src_cpu and dst_cpu may belong to the same group */
+ continue;
+ }
+
+ if (eenv->dst_cpu != -1 && cpumask_test_cpu(eenv->dst_cpu,
+ sched_group_cpus(sg))) {
+ eenv_before.sg_top = eenv->sg_top = sg;
+ energy_before += sched_group_energy(&eenv_before);
+ energy_after += sched_group_energy(eenv);
+ }
+ } while (sg = sg->next, sg != sd->groups);
+
+ return energy_after-energy_before;
+}
+
static int wake_wide(struct task_struct *p)
{
int factor = this_cpu_read(sd_llc_size);
--
1.9.1