Re: [PATCH 3/3] hmp: Use idle pull to perform forced up-migrations

Hi all,

Apologies for the missing coverletter. These are the patches Basil mentioned earlier today, all review comments gratefully received :)

I have just spotted a bug, so there might be a fix for that coming along tomorrow. I don't think it's critical yet, it can probably wait if we need to.

--Chris

On 13/03/14 17:19, Chris Redpath wrote:

When a normal forced up-migration takes place we stop the task to be migrated while the target CPU becomes available. This delay can range from 80us to 1500us on TC2 if the target CPU is in a deep idle state.

Instead, interrupt the target CPU and ask it to pull a task. This lets the current eligible task continue executing on the original CPU while the target CPU wakes. Use a pinned timer to prevent the pulling CPU going back into power-down with pending up-migrations.

If the target CPU is busy, we will not pull any tasks.

Signed-off-by: Chris Redpath chris.redpath@arm.com

kernel/sched/core.c | 18 +++++++++++- kernel/sched/fair.c | 74 ++++++++++++++++++++++++++++++++++++++++++-------- kernel/sched/sched.h | 1 + 3 files changed, 81 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index de9d360..89e49e1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1407,7 +1407,11 @@ void scheduler_ipi(void) { if (llist_empty(&this_rq()->wake_list) && !tick_nohz_full_cpu(smp_processor_id())

• 	&& !got_nohz_idle_kick())
  

• 	&& !got_nohz_idle_kick()
  

+#ifdef CONFIG_SCHED_HMP

• 	&& !this_rq()->wake_for_idle_pull
  

+#endif

• 	)
  

  return;

  /*

@@ -1430,10 +1434,22 @@ void scheduler_ipi(void) /* * Check if someone kicked us for doing the nohz idle load balance. */ +#ifdef CONFIG_SCHED_HMP

• {

• bool nohz = got_nohz_idle_kick();
  

• if (unlikely(this_rq()->wake_for_idle_pull) ||
  

• 	unlikely(nohz)) {
  

• 	if (unlikely(nohz))
  

• 		this_rq()->idle_balance = 1;
  

• 	raise_softirq_irqoff(SCHED_SOFTIRQ);
  

• }
  

• }

+#else if (unlikely(got_nohz_idle_kick())) { this_rq()->idle_balance = 1; raise_softirq_irqoff(SCHED_SOFTIRQ); } +#endif irq_exit(); }

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a5cae4a..d59e0de 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3541,6 +3541,43 @@ static const int hmp_max_tasks = 5;

extern void __init arch_get_hmp_domains(struct list_head *hmp_domains_list);

+struct hmp_keepalive {

• bool init;
• ktime_t delay;
• struct hrtimer timer;

+}; +DEFINE_PER_CPU(struct hmp_keepalive, hmp_cpu_keepalive);

+/* setup per-cpu keepalive timers */ +static enum hrtimer_restart hmp_cpu_keepalive_notify(struct hrtimer *hrtimer) +{

• return HRTIMER_NORESTART;

+}

+static inline void hmp_cpu_keepalive_init(struct hmp_keepalive *keepalive, int cpu) +{

• struct hrtimer *hrtimer;
• unsigned int ns_delay = 1000000;
• if (keepalive->init)

• return;
  

• /* make sure we only init for the right CPU */
• WARN_ON(keepalive != &per_cpu(hmp_cpu_keepalive, smp_processor_id()));
• hrtimer = &keepalive->timer;
• hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
• hrtimer->function = hmp_cpu_keepalive_notify;
• keepalive->delay = ns_to_ktime(ns_delay);
• keepalive->init = true;

+}

+static void hmp_cpu_keepalive_trigger(void) +{

• int cpu = smp_processor_id();
• struct hmp_keepalive *keepalive = &per_cpu(hmp_cpu_keepalive, cpu);
• hmp_cpu_keepalive_init(keepalive, cpu);
• hrtimer_start(&keepalive->timer, keepalive->delay, HRTIMER_MODE_REL_PINNED);

+}

• /* Setup hmp_domains */ static int __init hmp_cpu_mask_setup(void) {

@@ -3598,9 +3635,13 @@ static void hmp_online_cpu(int cpu) static void hmp_offline_cpu(int cpu) { struct hmp_domain *domain = hmp_get_hmp_domain_for_cpu(cpu);

• struct hmp_keepalive *keepalive = &per_cpu(hmp_cpu_keepalive, cpu);

  if(domain) cpumask_clear_cpu(cpu, &domain->cpus);

• if (keepalive->init)

• hrtimer_cancel(&keepalive->timer);
  

  } /*

  • Needed to determine heaviest tasks etc.

@@ -7021,7 +7062,7 @@ static void hmp_force_up_migration(int this_cpu) target = cpu_rq(cpu); raw_spin_lock_irqsave(&target->lock, flags); curr = target->cfs.curr;

• if (!curr) {
  

• if (!curr || target->active_balance) {
  raw_spin_unlock_irqrestore(&target->lock, flags);
  continue;
  

  }

@@ -7038,16 +7079,13 @@ static void hmp_force_up_migration(int this_cpu) curr = hmp_get_heaviest_task(curr, 1); p = task_of(curr); if (hmp_up_migration(cpu, &target_cpu, curr)) {

• 	if (!target->active_balance) {
  

• 		get_task_struct(p);
  

• 		target->push_cpu = target_cpu;
  

• 		target->migrate_task = p;
  

• 		got_target = 1;
  

• 		trace_sched_hmp_migrate(p, target->push_cpu, HMP_MIGRATE_FORCE);
  

• 		hmp_next_up_delay(&p->se, target->push_cpu);
  

• 	}
  

• 	cpu_rq(target_cpu)->wake_for_idle_pull = 1;
  

• 	raw_spin_unlock_irqrestore(&target->lock, flags);
  

• 	spin_unlock(&hmp_force_migration);
  

• 	smp_send_reschedule(target_cpu);
  

• 	return;
  

  }

• if (!got_target && !target->active_balance) {
  

• if (!got_target) {
  /*
   * For now we just check the currently running task.
   * Selecting the lightest task for offloading will
  

@@ -7069,7 +7107,7 @@ static void hmp_force_up_migration(int this_cpu) * is not currently running move it, otherwise let the * CPU stopper take care of it. */

• if (got_target && !target->active_balance) {
  

• if (got_target) {
  if (!task_running(target, p)) {
  	trace_sched_hmp_migrate_force_running(p, 0);
  	hmp_migrate_runnable_task(target);
  

@@ -7175,6 +7213,8 @@ static unsigned int hmp_idle_pull(int this_cpu) raw_spin_unlock_irqrestore(&target->lock, flags);

if (force) {

• /* start timer to keep us awake */
  

• hmp_cpu_keepalive_trigger();
  

  stop_one_cpu_nowait(cpu_of(target), hmp_active_task_migration_cpu_stop, target, &target->active_balance_work);

@@ -7198,6 +7238,18 @@ static void run_rebalance_domains(struct softirq_action *h) enum cpu_idle_type idle = this_rq->idle_balance ? CPU_IDLE : CPU_NOT_IDLE;

+#ifdef CONFIG_SCHED_HMP

• /* shortcut for hmp idle pull wakeups */
• if (unlikely(this_rq->wake_for_idle_pull)) {

• this_rq->wake_for_idle_pull = 0;
  

• if (hmp_idle_pull(this_cpu)) {
  

• 	/* break out unless running nohz idle as well */
  

• 	if (idle != CPU_IDLE)
  

• 		return;
  

• }
  

• }

+#endif

• hmp_force_up_migration(this_cpu);

  rebalance_domains(this_cpu, idle);

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 989c5ae..0d19ede 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -466,6 +466,7 @@ struct rq { struct cpu_stop_work active_balance_work; #ifdef CONFIG_SCHED_HMP struct task_struct *migrate_task;

• int wake_for_idle_pull; #endif /* cpu of this runqueue: */ int cpu;