#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/percpu.h>
-#include <linux/kthread.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
+#include <linux/stop_machine.h>
#include <linux/sysctl.h>
#include <linux/syscalls.h>
#include <linux/times.h>
int post_schedule;
int active_balance;
int push_cpu;
+ struct cpu_stop_work active_balance_work;
/* cpu of this runqueue: */
int cpu;
int online;
unsigned long avg_load_per_task;
- struct task_struct *migration_thread;
- struct list_head migration_queue;
-
u64 rt_avg;
u64 age_stamp;
u64 idle_stamp;
__set_task_cpu(p, new_cpu);
}
-struct migration_req {
- struct list_head list;
-
+struct migration_arg {
struct task_struct *task;
int dest_cpu;
-
- struct completion done;
};
+static int migration_cpu_stop(void *data);
+
/*
* The task's runqueue lock must be held.
* Returns true if you have to wait for migration thread.
*/
-static int
-migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
+static bool migrate_task(struct task_struct *p, int dest_cpu)
{
struct rq *rq = task_rq(p);
* If the task is not on a runqueue (and not running), then
* the next wake-up will properly place the task.
*/
- if (!p->se.on_rq && !task_running(rq, p))
- return 0;
-
- init_completion(&req->done);
- req->task = p;
- req->dest_cpu = dest_cpu;
- list_add(&req->list, &rq->migration_queue);
-
- return 1;
+ return p->se.on_rq || task_running(rq, p);
}
/*
void sched_exec(void)
{
struct task_struct *p = current;
- struct migration_req req;
unsigned long flags;
struct rq *rq;
int dest_cpu;
* select_task_rq() can race against ->cpus_allowed
*/
if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed) &&
- likely(cpu_active(dest_cpu)) &&
- migrate_task(p, dest_cpu, &req)) {
- /* Need to wait for migration thread (might exit: take ref). */
- struct task_struct *mt = rq->migration_thread;
+ likely(cpu_active(dest_cpu)) && migrate_task(p, dest_cpu)) {
+ struct migration_arg arg = { p, dest_cpu };
- get_task_struct(mt);
task_rq_unlock(rq, &flags);
- wake_up_process(mt);
- put_task_struct(mt);
- wait_for_completion(&req.done);
-
+ stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
return;
}
unlock:
/*
* This is how migration works:
*
- * 1) we queue a struct migration_req structure in the source CPU's
- * runqueue and wake up that CPU's migration thread.
- * 2) we down() the locked semaphore => thread blocks.
- * 3) migration thread wakes up (implicitly it forces the migrated
- * thread off the CPU)
- * 4) it gets the migration request and checks whether the migrated
- * task is still in the wrong runqueue.
- * 5) if it's in the wrong runqueue then the migration thread removes
+ * 1) we invoke migration_cpu_stop() on the target CPU using
+ * stop_one_cpu().
+ * 2) stopper starts to run (implicitly forcing the migrated thread
+ * off the CPU)
+ * 3) it checks whether the migrated task is still in the wrong runqueue.
+ * 4) if it's in the wrong runqueue then the migration thread removes
* it and puts it into the right queue.
- * 6) migration thread up()s the semaphore.
- * 7) we wake up and the migration is done.
+ * 5) stopper completes and stop_one_cpu() returns and the migration
+ * is done.
*/
/*
*/
int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
{
- struct migration_req req;
unsigned long flags;
struct rq *rq;
+ unsigned int dest_cpu;
int ret = 0;
/*
if (cpumask_test_cpu(task_cpu(p), new_mask))
goto out;
- if (migrate_task(p, cpumask_any_and(cpu_active_mask, new_mask), &req)) {
+ dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);
+ if (migrate_task(p, dest_cpu)) {
+ struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
- struct task_struct *mt = rq->migration_thread;
-
- get_task_struct(mt);
task_rq_unlock(rq, &flags);
- wake_up_process(mt);
- put_task_struct(mt);
- wait_for_completion(&req.done);
+ stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
tlb_migrate_finish(p->mm);
return 0;
}
return ret;
}
-#define RCU_MIGRATION_IDLE 0
-#define RCU_MIGRATION_NEED_QS 1
-#define RCU_MIGRATION_GOT_QS 2
-#define RCU_MIGRATION_MUST_SYNC 3
-
/*
- * migration_thread - this is a highprio system thread that performs
- * thread migration by bumping thread off CPU then 'pushing' onto
- * another runqueue.
+ * migration_cpu_stop - this will be executed by a highprio stopper thread
+ * and performs thread migration by bumping thread off CPU then
+ * 'pushing' onto another runqueue.
*/
-static int migration_thread(void *data)
+static int migration_cpu_stop(void *data)
{
- int badcpu;
- int cpu = (long)data;
- struct rq *rq;
-
- rq = cpu_rq(cpu);
- BUG_ON(rq->migration_thread != current);
-
- set_current_state(TASK_INTERRUPTIBLE);
- while (!kthread_should_stop()) {
- struct migration_req *req;
- struct list_head *head;
-
- raw_spin_lock_irq(&rq->lock);
-
- if (cpu_is_offline(cpu)) {
- raw_spin_unlock_irq(&rq->lock);
- break;
- }
-
- if (rq->active_balance) {
- active_load_balance(rq, cpu);
- rq->active_balance = 0;
- }
-
- head = &rq->migration_queue;
-
- if (list_empty(head)) {
- raw_spin_unlock_irq(&rq->lock);
- schedule();
- set_current_state(TASK_INTERRUPTIBLE);
- continue;
- }
- req = list_entry(head->next, struct migration_req, list);
- list_del_init(head->next);
-
- if (req->task != NULL) {
- raw_spin_unlock(&rq->lock);
- __migrate_task(req->task, cpu, req->dest_cpu);
- } else if (likely(cpu == (badcpu = smp_processor_id()))) {
- req->dest_cpu = RCU_MIGRATION_GOT_QS;
- raw_spin_unlock(&rq->lock);
- } else {
- req->dest_cpu = RCU_MIGRATION_MUST_SYNC;
- raw_spin_unlock(&rq->lock);
- WARN_ONCE(1, "migration_thread() on CPU %d, expected %d\n", badcpu, cpu);
- }
- local_irq_enable();
-
- complete(&req->done);
- }
- __set_current_state(TASK_RUNNING);
+ struct migration_arg *arg = data;
+ /*
+ * The original target cpu might have gone down and we might
+ * be on another cpu but it doesn't matter.
+ */
+ local_irq_disable();
+ __migrate_task(arg->task, raw_smp_processor_id(), arg->dest_cpu);
+ local_irq_enable();
return 0;
}
static int __cpuinit
migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
- struct task_struct *p;
int cpu = (long)hcpu;
unsigned long flags;
- struct rq *rq;
+ struct rq *rq = cpu_rq(cpu);
switch (action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
- p = kthread_create(migration_thread, hcpu, "migration/%d", cpu);
- if (IS_ERR(p))
- return NOTIFY_BAD;
- kthread_bind(p, cpu);
- /* Must be high prio: stop_machine expects to yield to it. */
- rq = task_rq_lock(p, &flags);
- __setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
- task_rq_unlock(rq, &flags);
- get_task_struct(p);
- cpu_rq(cpu)->migration_thread = p;
rq->calc_load_update = calc_load_update;
break;
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
- /* Strictly unnecessary, as first user will wake it. */
- wake_up_process(cpu_rq(cpu)->migration_thread);
-
/* Update our root-domain */
- rq = cpu_rq(cpu);
raw_spin_lock_irqsave(&rq->lock, flags);
if (rq->rd) {
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
break;
#ifdef CONFIG_HOTPLUG_CPU
- case CPU_UP_CANCELED:
- case CPU_UP_CANCELED_FROZEN:
- if (!cpu_rq(cpu)->migration_thread)
- break;
- /* Unbind it from offline cpu so it can run. Fall thru. */
- kthread_bind(cpu_rq(cpu)->migration_thread,
- cpumask_any(cpu_online_mask));
- kthread_stop(cpu_rq(cpu)->migration_thread);
- put_task_struct(cpu_rq(cpu)->migration_thread);
- cpu_rq(cpu)->migration_thread = NULL;
- break;
-
case CPU_DEAD:
case CPU_DEAD_FROZEN:
migrate_live_tasks(cpu);
- rq = cpu_rq(cpu);
- kthread_stop(rq->migration_thread);
- put_task_struct(rq->migration_thread);
- rq->migration_thread = NULL;
/* Idle task back to normal (off runqueue, low prio) */
raw_spin_lock_irq(&rq->lock);
deactivate_task(rq, rq->idle, 0);
migrate_nr_uninterruptible(rq);
BUG_ON(rq->nr_running != 0);
calc_global_load_remove(rq);
- /*
- * No need to migrate the tasks: it was best-effort if
- * they didn't take sched_hotcpu_mutex. Just wake up
- * the requestors.
- */
- raw_spin_lock_irq(&rq->lock);
- while (!list_empty(&rq->migration_queue)) {
- struct migration_req *req;
-
- req = list_entry(rq->migration_queue.next,
- struct migration_req, list);
- list_del_init(&req->list);
- raw_spin_unlock_irq(&rq->lock);
- complete(&req->done);
- raw_spin_lock_irq(&rq->lock);
- }
- raw_spin_unlock_irq(&rq->lock);
break;
case CPU_DYING:
case CPU_DYING_FROZEN:
/* Update our root-domain */
- rq = cpu_rq(cpu);
raw_spin_lock_irqsave(&rq->lock, flags);
if (rq->rd) {
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
rq->push_cpu = 0;
rq->cpu = i;
rq->online = 0;
- rq->migration_thread = NULL;
rq->idle_stamp = 0;
rq->avg_idle = 2*sysctl_sched_migration_cost;
- INIT_LIST_HEAD(&rq->migration_queue);
rq_attach_root(rq, &def_root_domain);
#endif
init_rq_hrtick(rq);
#ifndef CONFIG_SMP
-int rcu_expedited_torture_stats(char *page)
-{
- return 0;
-}
-EXPORT_SYMBOL_GPL(rcu_expedited_torture_stats);
-
void synchronize_sched_expedited(void)
{
+ /*
+ * There must be a full memory barrier on each affected CPU
+ * between the time that try_stop_cpus() is called and the
+ * time that it returns.
+ *
+ * In the current initial implementation of cpu_stop, the
+ * above condition is already met when the control reaches
+ * this point and the following smp_mb() is not strictly
+ * necessary. Do smp_mb() anyway for documentation and
+ * robustness against future implementation changes.
+ */
+ smp_mb();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
#else /* #ifndef CONFIG_SMP */
-static DEFINE_PER_CPU(struct migration_req, rcu_migration_req);
-static DEFINE_MUTEX(rcu_sched_expedited_mutex);
-
-#define RCU_EXPEDITED_STATE_POST -2
-#define RCU_EXPEDITED_STATE_IDLE -1
+static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0);
-static int rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
-
-int rcu_expedited_torture_stats(char *page)
+static int synchronize_sched_expedited_cpu_stop(void *data)
{
- int cnt = 0;
- int cpu;
+ static DEFINE_SPINLOCK(done_mask_lock);
+ struct cpumask *done_mask = data;
- cnt += sprintf(&page[cnt], "state: %d /", rcu_expedited_state);
- for_each_online_cpu(cpu) {
- cnt += sprintf(&page[cnt], " %d:%d",
- cpu, per_cpu(rcu_migration_req, cpu).dest_cpu);
+ if (done_mask) {
+ spin_lock(&done_mask_lock);
+ cpumask_set_cpu(smp_processor_id(), done_mask);
+ spin_unlock(&done_mask_lock);
}
- cnt += sprintf(&page[cnt], "\n");
- return cnt;
+ return 0;
}
-EXPORT_SYMBOL_GPL(rcu_expedited_torture_stats);
-
-static long synchronize_sched_expedited_count;
/*
* Wait for an rcu-sched grace period to elapse, but use "big hammer"
*/
void synchronize_sched_expedited(void)
{
- int cpu;
- unsigned long flags;
- bool need_full_sync = 0;
- struct rq *rq;
- struct migration_req *req;
- long snap;
- int trycount = 0;
+ cpumask_var_t done_mask_var;
+ struct cpumask *done_mask = NULL;
+ int snap, trycount = 0;
+
+ /*
+ * done_mask is used to check that all cpus actually have
+ * finished running the stopper, which is guaranteed by
+ * stop_cpus() if it's called with cpu hotplug blocked. Keep
+ * the paranoia for now but it's best effort if cpumask is off
+ * stack.
+ */
+ if (zalloc_cpumask_var(&done_mask_var, GFP_ATOMIC))
+ done_mask = done_mask_var;
smp_mb(); /* ensure prior mod happens before capturing snap. */
- snap = ACCESS_ONCE(synchronize_sched_expedited_count) + 1;
+ snap = atomic_read(&synchronize_sched_expedited_count) + 1;
get_online_cpus();
- while (!mutex_trylock(&rcu_sched_expedited_mutex)) {
+ while (try_stop_cpus(cpu_online_mask,
+ synchronize_sched_expedited_cpu_stop,
+ done_mask) == -EAGAIN) {
put_online_cpus();
if (trycount++ < 10)
udelay(trycount * num_online_cpus());
else {
synchronize_sched();
- return;
+ goto free_out;
}
- if (ACCESS_ONCE(synchronize_sched_expedited_count) - snap > 0) {
+ if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {
smp_mb(); /* ensure test happens before caller kfree */
- return;
+ goto free_out;
}
get_online_cpus();
}
- rcu_expedited_state = RCU_EXPEDITED_STATE_POST;
- for_each_online_cpu(cpu) {
- rq = cpu_rq(cpu);
- req = &per_cpu(rcu_migration_req, cpu);
- init_completion(&req->done);
- req->task = NULL;
- req->dest_cpu = RCU_MIGRATION_NEED_QS;
- raw_spin_lock_irqsave(&rq->lock, flags);
- list_add(&req->list, &rq->migration_queue);
- raw_spin_unlock_irqrestore(&rq->lock, flags);
- wake_up_process(rq->migration_thread);
- }
- for_each_online_cpu(cpu) {
- rcu_expedited_state = cpu;
- req = &per_cpu(rcu_migration_req, cpu);
- rq = cpu_rq(cpu);
- wait_for_completion(&req->done);
- raw_spin_lock_irqsave(&rq->lock, flags);
- if (unlikely(req->dest_cpu == RCU_MIGRATION_MUST_SYNC))
- need_full_sync = 1;
- req->dest_cpu = RCU_MIGRATION_IDLE;
- raw_spin_unlock_irqrestore(&rq->lock, flags);
- }
- rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
- synchronize_sched_expedited_count++;
- mutex_unlock(&rcu_sched_expedited_mutex);
+ atomic_inc(&synchronize_sched_expedited_count);
+ if (done_mask)
+ cpumask_xor(done_mask, done_mask, cpu_online_mask);
put_online_cpus();
- if (need_full_sync)
+
+ /* paranoia - this can't happen */
+ if (done_mask && cpumask_weight(done_mask)) {
+ char buf[80];
+
+ cpulist_scnprintf(buf, sizeof(buf), done_mask);
+ WARN_ONCE(1, "synchronize_sched_expedited: cpu online and done masks disagree on %d cpus: %s\n",
+ cpumask_weight(done_mask), buf);
synchronize_sched();
+ }
+free_out:
+ free_cpumask_var(done_mask_var);
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}
+static int active_load_balance_cpu_stop(void *data);
+
/*
* Check this_cpu to ensure it is balanced within domain. Attempt to move
* tasks if there is an imbalance.
if (need_active_balance(sd, sd_idle, idle)) {
raw_spin_lock_irqsave(&busiest->lock, flags);
- /* don't kick the migration_thread, if the curr
- * task on busiest cpu can't be moved to this_cpu
+ /* don't kick the active_load_balance_cpu_stop,
+ * if the curr task on busiest cpu can't be
+ * moved to this_cpu
*/
if (!cpumask_test_cpu(this_cpu,
&busiest->curr->cpus_allowed)) {
goto out_one_pinned;
}
+ /*
+ * ->active_balance synchronizes accesses to
+ * ->active_balance_work. Once set, it's cleared
+ * only after active load balance is finished.
+ */
if (!busiest->active_balance) {
busiest->active_balance = 1;
busiest->push_cpu = this_cpu;
active_balance = 1;
}
raw_spin_unlock_irqrestore(&busiest->lock, flags);
+
if (active_balance)
- wake_up_process(busiest->migration_thread);
+ stop_one_cpu_nowait(cpu_of(busiest),
+ active_load_balance_cpu_stop, busiest,
+ &busiest->active_balance_work);
/*
* We've kicked active balancing, reset the failure
}
/*
- * active_load_balance is run by migration threads. It pushes running tasks
- * off the busiest CPU onto idle CPUs. It requires at least 1 task to be
- * running on each physical CPU where possible, and avoids physical /
- * logical imbalances.
- *
- * Called with busiest_rq locked.
+ * active_load_balance_cpu_stop is run by cpu stopper. It pushes
+ * running tasks off the busiest CPU onto idle CPUs. It requires at
+ * least 1 task to be running on each physical CPU where possible, and
+ * avoids physical / logical imbalances.
*/
-static void active_load_balance(struct rq *busiest_rq, int busiest_cpu)
+static int active_load_balance_cpu_stop(void *data)
{
+ struct rq *busiest_rq = data;
+ int busiest_cpu = cpu_of(busiest_rq);
int target_cpu = busiest_rq->push_cpu;
+ struct rq *target_rq = cpu_rq(target_cpu);
struct sched_domain *sd;
- struct rq *target_rq;
+
+ raw_spin_lock_irq(&busiest_rq->lock);
+
+ /* make sure the requested cpu hasn't gone down in the meantime */
+ if (unlikely(busiest_cpu != smp_processor_id() ||
+ !busiest_rq->active_balance))
+ goto out_unlock;
/* Is there any task to move? */
if (busiest_rq->nr_running <= 1)
- return;
-
- target_rq = cpu_rq(target_cpu);
+ goto out_unlock;
/*
* This condition is "impossible", if it occurs
schedstat_inc(sd, alb_failed);
}
double_unlock_balance(busiest_rq, target_rq);
+out_unlock:
+ busiest_rq->active_balance = 0;
+ raw_spin_unlock_irq(&busiest_rq->lock);
+ return 0;
}
#ifdef CONFIG_NO_HZ
git://ftp.safe.ca / safe / jmp / linux-2.6 / commitdiff