Commit 7961cf80 authored by Morten Rasmussen's avatar Morten Rasmussen
Browse files

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's avatarMorten Rasmussen <morten.rasmussen@arm.com>
parent 95c58189
......@@ -4609,25 +4609,27 @@ 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),
......@@ -4639,6 +4641,7 @@ 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 */
......@@ -4648,44 +4651,81 @@ 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 capacity of the group */
avg_load = (avg_load * SCHED_CAPACITY_SCALE) / group->sgc->capacity;
/*
* 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;
}
......@@ -4808,13 +4848,13 @@ 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;
......
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment