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Date: Fri, 23 May 2014 19:16:42 +0100
From: Morten Rasmussen <morten.rasmussen@....com>
To: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
peterz@...radead.org, mingo@...nel.org
Cc: rjw@...ysocki.net, vincent.guittot@...aro.org,
daniel.lezcano@...aro.org, preeti@...ux.vnet.ibm.com,
dietmar.eggemann@....com
Subject: [RFC PATCH 15/16] sched: Use energy to guide wakeup task placement
Attempt to pick most energy efficient wakeup in find_idlest_{group,
cpu}(). Finding the optimum target requires an exhaustive search
through all cpus in the groups. Instead, the target group is determined
based on load and probing the energy cost on a single cpu in each group.
The target cpu is the cpu with the lowest energy cost.
Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
---
kernel/sched/fair.c | 64 +++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 52 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 542c2b2..0d3334b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4556,25 +4556,27 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
}
/*
- * find_idlest_group finds and returns the least busy CPU group within the
- * domain.
+ * find_target_group finds and returns the least busy/most energy-efficient
+ * CPU group within the domain.
*/
static struct sched_group *
-find_idlest_group(struct sched_domain *sd, struct task_struct *p,
+find_target_group(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int sd_flag)
{
- struct sched_group *idlest = NULL, *group = sd->groups;
+ struct sched_group *idlest = NULL, *group = sd->groups, *energy = NULL;
unsigned long min_load = ULONG_MAX, this_load = 0;
int load_idx = sd->forkexec_idx;
int imbalance = 100 + (sd->imbalance_pct-100)/2;
+ int local_energy = 0, min_energy = INT_MAX;
if (sd_flag & SD_BALANCE_WAKE)
load_idx = sd->wake_idx;
do {
- unsigned long load, avg_load;
+ unsigned long load, avg_load, probe_load = UINT_MAX;
int local_group;
int i;
+ int probe_cpu, energy_diff;
/* Skip over this group if it has no CPUs allowed */
if (!cpumask_intersects(sched_group_cpus(group),
@@ -4586,6 +4588,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
/* Tally up the load of all CPUs in the group */
avg_load = 0;
+ probe_cpu = cpumask_first(sched_group_cpus(group));
for_each_cpu(i, sched_group_cpus(group)) {
/* Bias balancing toward cpus of our domain */
@@ -4595,44 +4598,81 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
load = target_load(i, load_idx);
avg_load += load;
+
+ if (load < probe_load) {
+ probe_load = load;
+ probe_cpu = i;
+ }
}
/* Adjust by relative CPU power of the group */
avg_load = (avg_load * SCHED_POWER_SCALE) / group->sgp->power;
+ /*
+ * Sample energy diff on probe_cpu.
+ * Finding the optimum cpu requires testing all cpus which is
+ * expensive.
+ */
+
+ energy_diff = energy_diff_task(probe_cpu, p);
+
if (local_group) {
this_load = avg_load;
- } else if (avg_load < min_load) {
- min_load = avg_load;
- idlest = group;
+ local_energy = energy_diff;
+ } else {
+ if (avg_load < min_load) {
+ min_load = avg_load;
+ idlest = group;
+ }
+
+ if (energy_diff < min_energy) {
+ min_energy = energy_diff;
+ energy = group;
+ }
}
} while (group = group->next, group != sd->groups);
+#ifdef CONFIG_SCHED_ENERGY
+ if (energy && min_energy < local_energy)
+ return energy;
+ return NULL;
+#else
if (!idlest || 100*this_load < imbalance*min_load)
return NULL;
return idlest;
+#endif
}
/*
- * find_idlest_cpu - find the idlest cpu among the cpus in group.
+ * find_target_cpu - find the target cpu among the cpus in group.
*/
static int
-find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
+find_target_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
{
unsigned long load, min_load = ULONG_MAX;
+ int min_energy = INT_MAX, energy, least_energy = -1;
int idlest = -1;
int i;
/* Traverse only the allowed CPUs */
for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
load = weighted_cpuload(i);
+ energy = energy_diff_task(i, p);
if (load < min_load || (load == min_load && i == this_cpu)) {
min_load = load;
idlest = i;
}
+
+ if (energy < min_energy) {
+ min_energy = energy;
+ least_energy = i;
+ }
}
+ if (least_energy >= 0)
+ return least_energy;
+
return idlest;
}
@@ -4755,13 +4795,13 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
continue;
}
- group = find_idlest_group(sd, p, cpu, sd_flag);
+ group = find_target_group(sd, p, cpu, sd_flag);
if (!group) {
sd = sd->child;
continue;
}
- new_cpu = find_idlest_cpu(group, p, cpu);
+ new_cpu = find_target_cpu(group, p, cpu);
if (new_cpu == -1 || new_cpu == cpu) {
/* Now try balancing at a lower domain level of cpu */
sd = sd->child;
--
1.7.9.5
--
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