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.rasmussen@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),