#ifdef CONFIG_SMP
unsigned long cpu_load[3];
unsigned char idle_at_tick;
+#ifdef CONFIG_NO_HZ
+ unsigned char in_nohz_recently;
+#endif
#endif
unsigned long long nr_switches;
if (!tsk_is_polling(p))
smp_send_reschedule(cpu);
}
+
+static void resched_cpu(int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+ unsigned long flags;
+
+ if (!spin_trylock_irqsave(&rq->lock, flags))
+ return;
+ resched_task(cpu_curr(cpu));
+ spin_unlock_irqrestore(&rq->lock, flags);
+}
#else
static inline void resched_task(struct task_struct *p)
{
double_rq_unlock(this_rq, busiest);
local_irq_restore(flags);
+ /*
+ * some other cpu did the load balance for us.
+ */
+ if (nr_moved && this_cpu != smp_processor_id())
+ resched_cpu(this_cpu);
+
/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(all_pinned)) {
cpu_clear(cpu_of(busiest), cpus);
}
}
+#ifdef CONFIG_NO_HZ
+static struct {
+ atomic_t load_balancer;
+ cpumask_t cpu_mask;
+} nohz ____cacheline_aligned = {
+ .load_balancer = ATOMIC_INIT(-1),
+ .cpu_mask = CPU_MASK_NONE,
+};
+
/*
- * run_rebalance_domains is triggered when needed from the scheduler tick.
+ * This routine will try to nominate the ilb (idle load balancing)
+ * owner among the cpus whose ticks are stopped. ilb owner will do the idle
+ * load balancing on behalf of all those cpus. If all the cpus in the system
+ * go into this tickless mode, then there will be no ilb owner (as there is
+ * no need for one) and all the cpus will sleep till the next wakeup event
+ * arrives...
+ *
+ * For the ilb owner, tick is not stopped. And this tick will be used
+ * for idle load balancing. ilb owner will still be part of
+ * nohz.cpu_mask..
+ *
+ * While stopping the tick, this cpu will become the ilb owner if there
+ * is no other owner. And will be the owner till that cpu becomes busy
+ * or if all cpus in the system stop their ticks at which point
+ * there is no need for ilb owner.
*
+ * When the ilb owner becomes busy, it nominates another owner, during the
+ * next busy scheduler_tick()
+ */
+int select_nohz_load_balancer(int stop_tick)
+{
+ int cpu = smp_processor_id();
+
+ if (stop_tick) {
+ cpu_set(cpu, nohz.cpu_mask);
+ cpu_rq(cpu)->in_nohz_recently = 1;
+
+ /*
+ * If we are going offline and still the leader, give up!
+ */
+ if (cpu_is_offline(cpu) &&
+ atomic_read(&nohz.load_balancer) == cpu) {
+ if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
+ BUG();
+ return 0;
+ }
+
+ /* time for ilb owner also to sleep */
+ if (cpus_weight(nohz.cpu_mask) == num_online_cpus()) {
+ if (atomic_read(&nohz.load_balancer) == cpu)
+ atomic_set(&nohz.load_balancer, -1);
+ return 0;
+ }
+
+ if (atomic_read(&nohz.load_balancer) == -1) {
+ /* make me the ilb owner */
+ if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) == -1)
+ return 1;
+ } else if (atomic_read(&nohz.load_balancer) == cpu)
+ return 1;
+ } else {
+ if (!cpu_isset(cpu, nohz.cpu_mask))
+ return 0;
+
+ cpu_clear(cpu, nohz.cpu_mask);
+
+ if (atomic_read(&nohz.load_balancer) == cpu)
+ if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
+ BUG();
+ }
+ return 0;
+}
+#endif
+
+static DEFINE_SPINLOCK(balancing);
+
+/*
* It checks each scheduling domain to see if it is due to be balanced,
* and initiates a balancing operation if so.
*
* Balancing parameters are set up in arch_init_sched_domains.
*/
-static DEFINE_SPINLOCK(balancing);
-
-static void run_rebalance_domains(struct softirq_action *h)
+static inline void rebalance_domains(int cpu, enum idle_type idle)
{
- int this_cpu = smp_processor_id(), balance = 1;
- struct rq *this_rq = cpu_rq(this_cpu);
+ int balance = 1;
+ struct rq *rq = cpu_rq(cpu);
unsigned long interval;
struct sched_domain *sd;
- enum idle_type idle = this_rq->idle_at_tick ? SCHED_IDLE : NOT_IDLE;
- /* Earliest time when we have to call run_rebalance_domains again */
+ /* Earliest time when we have to do rebalance again */
unsigned long next_balance = jiffies + 60*HZ;
- for_each_domain(this_cpu, sd) {
+ for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
continue;
}
if (time_after_eq(jiffies, sd->last_balance + interval)) {
- if (load_balance(this_cpu, this_rq, sd, idle, &balance)) {
+ if (load_balance(cpu, rq, sd, idle, &balance)) {
/*
* We've pulled tasks over so either we're no
* longer idle, or one of our SMT siblings is
if (!balance)
break;
}
- this_rq->next_balance = next_balance;
+ rq->next_balance = next_balance;
+}
+
+/*
+ * run_rebalance_domains is triggered when needed from the scheduler tick.
+ * In CONFIG_NO_HZ case, the idle load balance owner will do the
+ * rebalancing for all the cpus for whom scheduler ticks are stopped.
+ */
+static void run_rebalance_domains(struct softirq_action *h)
+{
+ int local_cpu = smp_processor_id();
+ struct rq *local_rq = cpu_rq(local_cpu);
+ enum idle_type idle = local_rq->idle_at_tick ? SCHED_IDLE : NOT_IDLE;
+
+ rebalance_domains(local_cpu, idle);
+
+#ifdef CONFIG_NO_HZ
+ /*
+ * If this cpu is the owner for idle load balancing, then do the
+ * balancing on behalf of the other idle cpus whose ticks are
+ * stopped.
+ */
+ if (local_rq->idle_at_tick &&
+ atomic_read(&nohz.load_balancer) == local_cpu) {
+ cpumask_t cpus = nohz.cpu_mask;
+ struct rq *rq;
+ int balance_cpu;
+
+ cpu_clear(local_cpu, cpus);
+ for_each_cpu_mask(balance_cpu, cpus) {
+ /*
+ * If this cpu gets work to do, stop the load balancing
+ * work being done for other cpus. Next load
+ * balancing owner will pick it up.
+ */
+ if (need_resched())
+ break;
+
+ rebalance_domains(balance_cpu, SCHED_IDLE);
+
+ rq = cpu_rq(balance_cpu);
+ if (time_after(local_rq->next_balance, rq->next_balance))
+ local_rq->next_balance = rq->next_balance;
+ }
+ }
+#endif
+}
+
+/*
+ * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
+ *
+ * In case of CONFIG_NO_HZ, this is the place where we nominate a new
+ * idle load balancing owner or decide to stop the periodic load balancing,
+ * if the whole system is idle.
+ */
+static inline void trigger_load_balance(int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+#ifdef CONFIG_NO_HZ
+ /*
+ * If we were in the nohz mode recently and busy at the current
+ * scheduler tick, then check if we need to nominate new idle
+ * load balancer.
+ */
+ if (rq->in_nohz_recently && !rq->idle_at_tick) {
+ rq->in_nohz_recently = 0;
+
+ if (atomic_read(&nohz.load_balancer) == cpu) {
+ cpu_clear(cpu, nohz.cpu_mask);
+ atomic_set(&nohz.load_balancer, -1);
+ }
+
+ if (atomic_read(&nohz.load_balancer) == -1) {
+ /*
+ * simple selection for now: Nominate the
+ * first cpu in the nohz list to be the next
+ * ilb owner.
+ *
+ * TBD: Traverse the sched domains and nominate
+ * the nearest cpu in the nohz.cpu_mask.
+ */
+ int ilb = first_cpu(nohz.cpu_mask);
+
+ if (ilb != NR_CPUS)
+ resched_cpu(ilb);
+ }
+ }
+
+ /*
+ * If this cpu is idle and doing idle load balancing for all the
+ * cpus with ticks stopped, is it time for that to stop?
+ */
+ if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) == cpu &&
+ cpus_weight(nohz.cpu_mask) == num_online_cpus()) {
+ resched_cpu(cpu);
+ return;
+ }
+
+ /*
+ * If this cpu is idle and the idle load balancing is done by
+ * someone else, then no need raise the SCHED_SOFTIRQ
+ */
+ if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) != cpu &&
+ cpu_isset(cpu, nohz.cpu_mask))
+ return;
+#endif
+ if (time_after_eq(jiffies, rq->next_balance))
+ raise_softirq(SCHED_SOFTIRQ);
}
#else
/*
#ifdef CONFIG_SMP
update_load(rq);
rq->idle_at_tick = idle_at_tick;
- if (time_after_eq(jiffies, rq->next_balance))
- raise_softirq(SCHED_SOFTIRQ);
+ trigger_load_balance(cpu);
#endif
}
projects / powerpc.git / blobdiff