This patch introduces an extra-check at task up-migration to
prevent overloading the cpus in the faster hmp_domain while the
slower hmp_domain is not fully utilized. The patch also introduces
a periodic balance check that can down-migrate tasks if the faster
domain is oversubscribed and the slower is under-utilized.
Signed-off-by: Morten Rasmussen <morten.rasmus...@arm.com>
---
kernel/sched/fair.c | 101 +++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 97 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1cfe112..7ac47c9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3249,6 +3249,80 @@ static inline void hmp_next_down_delay(struct
sched_entity *se, int cpu)
se->avg.hmp_last_down_migration = cfs_rq_clock_task(cfs_rq);
se->avg.hmp_last_up_migration = 0;
}
+
+static inline unsigned int hmp_domain_min_load(struct hmp_domain *hmpd,
+ int *min_cpu)
+{
+ int cpu;
+ int min_load = INT_MAX;
+ int min_cpu_temp = NR_CPUS;
+
+ for_each_cpu_mask(cpu, hmpd->cpus) {
+ if (cpu_rq(cpu)->cfs.tg_load_contrib < min_load) {
+ min_load = cpu_rq(cpu)->cfs.tg_load_contrib;
+ min_cpu_temp = cpu;
+ }
+ }
+
+ if (min_cpu)
+ *min_cpu = min_cpu_temp;
+
+ return min_load;
+}
+
+/*
+ * Calculate the task starvation
+ * This is the ratio of actually running time vs. runnable time.
+ * If the two are equal the task is getting the cpu time it needs or
+ * it is alone on the cpu and the cpu is fully utilized.
+ */
+static inline unsigned int hmp_task_starvation(struct sched_entity *se)
+{
+ u32 starvation;
+
+ starvation = se->avg.usage_avg_sum * scale_load_down(NICE_0_LOAD);
+ starvation /= (se->avg.runnable_avg_sum + 1);
+
+ return scale_load(starvation);
+}
+
+static inline unsigned int hmp_offload_down(int cpu, struct sched_entity *se)
+{
+ int min_usage;
+ int dest_cpu = NR_CPUS;
+
+ if (hmp_cpu_is_slowest(cpu))
+ return NR_CPUS;
+
+ /* Is the current domain fully loaded? */
+ /* load < ~94% */
+ min_usage = hmp_domain_min_load(hmp_cpu_domain(cpu), NULL);
+ if (min_usage < NICE_0_LOAD-64)
+ return NR_CPUS;
+
+ /* Is the cpu oversubscribed? */
+ /* load < ~194% */
+ if (cpu_rq(cpu)->cfs.tg_load_contrib < 2*NICE_0_LOAD-64)
+ return NR_CPUS;
+
+ /* Is the task alone on the cpu? */
+ if (cpu_rq(cpu)->cfs.nr_running < 2)
+ return NR_CPUS;
+
+ /* Is the task actually starving? */
+ if (hmp_task_starvation(se) > 768) /* <25% waiting */
+ return NR_CPUS;
+
+ /* Does the slower domain have spare cycles? */
+ min_usage = hmp_domain_min_load(hmp_slower_domain(cpu), &dest_cpu);
+ /* load > 50% */
+ if (min_usage > NICE_0_LOAD/2)
+ return NR_CPUS;
+
+ if (cpumask_test_cpu(dest_cpu, &hmp_slower_domain(cpu)->cpus))
+ return dest_cpu;
+ return NR_CPUS;
+}
#endif /* CONFIG_SCHED_HMP */
/*
@@ -5643,10 +5717,14 @@ static unsigned int hmp_up_migration(int cpu, struct
sched_entity *se)
< hmp_next_up_threshold)
return 0;
- if (se->avg.load_avg_ratio > hmp_up_threshold &&
- cpumask_intersects(&hmp_faster_domain(cpu)->cpus,
- tsk_cpus_allowed(p))) {
- return 1;
+ if (se->avg.load_avg_ratio > hmp_up_threshold) {
+ /* Target domain load < ~94% */
+ if (hmp_domain_min_load(hmp_faster_domain(cpu), NULL)
+ > NICE_0_LOAD-64)
+ return 0;
+ if (cpumask_intersects(&hmp_faster_domain(cpu)->cpus,
+ tsk_cpus_allowed(p)))
+ return 1;
}
return 0;
}
@@ -5868,6 +5946,21 @@ static void hmp_force_up_migration(int this_cpu)
hmp_next_up_delay(&p->se, target->push_cpu);
}
}
+ if (!force && !target->active_balance) {
+ /*
+ * For now we just check the currently running task.
+ * Selecting the lightest task for offloading will
+ * require extensive book keeping.
+ */
+ target->push_cpu = hmp_offload_down(cpu, curr);
+ if (target->push_cpu < NR_CPUS) {
+ target->active_balance = 1;
+ target->migrate_task = p;
+ force = 1;
+ trace_sched_hmp_migrate(p, target->push_cpu, 2);
+ hmp_next_down_delay(&p->se, target->push_cpu);
+ }
+ }
raw_spin_unlock_irqrestore(&target->lock, flags);
if (force)
stop_one_cpu_nowait(cpu_of(target),
--
1.7.9.5
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