During the creation of sched_domain, we define a pack buddy CPU for each CPU
when one is available. We want to pack at all levels where a group of CPUs can
be power gated independently from others.
On a system that can't power gate a group of CPUs independently, the flag is
set at all sched_domain level and the buddy is set to -1. This is the default
behavior for all architectures.
On a dual clusters / dual cores system which can power gate each core and
cluster independently, the buddy configuration will be :
| Cluster 0 | Cluster 1 |
| CPU0 | CPU1 | CPU2 | CPU3 |
-----------------------------------
buddy | CPU0 | CPU0 | CPU0 | CPU2 |
If the cores in a cluster can't be power gated independently, the buddy
configuration becomes:
| Cluster 0 | Cluster 1 |
| CPU0 | CPU1 | CPU2 | CPU3 |
-----------------------------------
buddy | CPU0 | CPU1 | CPU0 | CPU0 |
Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
---
kernel/sched/core.c | 1 +
kernel/sched/fair.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++
kernel/sched/sched.h | 5 ++++
3 files changed, 76 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 735e964..0bf5f4d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5184,6 +5184,7 @@ cpu_attach_domain(struct sched_domain *sd, struct
root_domain *rd, int cpu)
rcu_assign_pointer(rq->sd, sd);
destroy_sched_domains(tmp, cpu);
+ update_packing_domain(cpu);
update_top_cache_domain(cpu);
}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 11cd136..5547831 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -178,6 +178,76 @@ void sched_init_granularity(void)
update_sysctl();
}
+#ifdef CONFIG_SMP
+#ifdef CONFIG_SCHED_PACKING_TASKS
+/*
+ * Save the id of the optimal CPU that should be used to pack small tasks
+ * The value -1 is used when no buddy has been found
+ */
+DEFINE_PER_CPU(int, sd_pack_buddy);
+
+/*
+ * Look for the best buddy CPU that can be used to pack small tasks
+ * We make the assumption that it doesn't wort to pack on CPU that share the
+ * same powerline. We look for the 1st sched_domain without the
+ * SD_SHARE_POWERDOMAIN flag. Then we look for the sched_group with the lowest
+ * power per core based on the assumption that their power efficiency is
+ * better
+ */
+void update_packing_domain(int cpu)
+{
+ struct sched_domain *sd;
+ int id = -1;
+
+ sd = highest_flag_domain(cpu, SD_SHARE_POWERDOMAIN);
+ if (!sd)
+ sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd);
+ else
+ sd = sd->parent;
+
+ while (sd && (sd->flags & SD_LOAD_BALANCE)
+ && !(sd->flags & SD_SHARE_POWERDOMAIN)) {
+ struct sched_group *sg = sd->groups;
+ struct sched_group *pack = sg;
+ struct sched_group *tmp;
+
+ /*
+ * The sched_domain of a CPU points on the local sched_group
+ * and this CPU of this local group is a good candidate
+ */
+ id = cpu;
+
+ /* loop the sched groups to find the best one */
+ for (tmp = sg->next; tmp != sg; tmp = tmp->next) {
+ if (tmp->sgp->power * pack->group_weight >
+ pack->sgp->power * tmp->group_weight)
+ continue;
+
+ if ((tmp->sgp->power * pack->group_weight ==
+ pack->sgp->power * tmp->group_weight)
+ && (cpumask_first(sched_group_cpus(tmp)) >= id))
+ continue;
+
+ /* we have found a better group */
+ pack = tmp;
+
+ /* Take the 1st CPU of the new group */
+ id = cpumask_first(sched_group_cpus(pack));
+ }
+
+ /* Look for another CPU than itself */
+ if (id != cpu)
+ break;
+
+ sd = sd->parent;
+ }
+
+ pr_debug("CPU%d packing on CPU%d\n", cpu, id);
+ per_cpu(sd_pack_buddy, cpu) = id;
+}
+#endif /* CONFIG_SCHED_PACKING_TASKS */
+#endif /* CONFIG_SMP */
+
#if BITS_PER_LONG == 32
# define WMULT_CONST (~0UL)
#else
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b3c5653..22e3f1d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1022,6 +1022,11 @@ extern void update_group_power(struct sched_domain *sd,
int cpu);
extern void trigger_load_balance(struct rq *rq, int cpu);
extern void idle_balance(int this_cpu, struct rq *this_rq);
+#ifdef CONFIG_SCHED_PACKING_TASKS
+extern void update_packing_domain(int cpu);
+#else
+static inline void update_packing_domain(int cpu) {};
+#endif
extern void idle_enter_fair(struct rq *this_rq);
extern void idle_exit_fair(struct rq *this_rq);
--
1.7.9.5
--
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