Messages in this thread Patch in this message | | | From | Morten Rasmussen <> | Subject | [RFC PATCH 15/16] sched: Use energy to guide wakeup task placement | Date | Fri, 23 May 2014 19:16:42 +0100 |
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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@arm.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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