if (current->policy == SCHED_RR) {
struct sched_rt_entity *rt_se = ¤t->rt;
- return rt_se->run_list.prev == rt_se->run_list.next;
+ return list_is_singular(&rt_se->run_list);
}
/*
return;
}
- load->weight = scale_load(prio_to_weight[prio]);
- load->inv_weight = prio_to_wmult[prio];
+ load->weight = scale_load(sched_prio_to_weight[prio]);
+ load->inv_weight = sched_prio_to_wmult[prio];
}
static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
lockdep_assert_held(&rq->lock);
- dequeue_task(rq, p, 0);
p->on_rq = TASK_ON_RQ_MIGRATING;
+ dequeue_task(rq, p, 0);
set_task_cpu(p, new_cpu);
raw_spin_unlock(&rq->lock);
raw_spin_lock(&rq->lock);
BUG_ON(task_cpu(p) != new_cpu);
- p->on_rq = TASK_ON_RQ_QUEUED;
enqueue_task(rq, p, 0);
+ p->on_rq = TASK_ON_RQ_QUEUED;
check_preempt_curr(rq, p, 0);
return rq;
WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
!p->on_rq);
+ /*
+ * Migrating fair class task must have p->on_rq = TASK_ON_RQ_MIGRATING,
+ * because schedstat_wait_{start,end} rebase migrating task's wait_start
+ * time relying on p->on_rq.
+ */
+ WARN_ON_ONCE(p->state == TASK_RUNNING &&
+ p->sched_class == &fair_sched_class &&
+ (p->on_rq && !task_on_rq_migrating(p)));
+
#ifdef CONFIG_LOCKDEP
/*
* The caller should hold either p->pi_lock or rq->lock, when changing
src_rq = task_rq(p);
dst_rq = cpu_rq(cpu);
+ p->on_rq = TASK_ON_RQ_MIGRATING;
deactivate_task(src_rq, p, 0);
set_task_cpu(p, cpu);
activate_task(dst_rq, p, 0);
+ p->on_rq = TASK_ON_RQ_QUEUED;
check_preempt_curr(dst_rq, p, 0);
} else {
/*
raw_spin_unlock(&rq->lock);
}
+/*
+ * Notes on Program-Order guarantees on SMP systems.
+ *
+ * MIGRATION
+ *
+ * The basic program-order guarantee on SMP systems is that when a task [t]
+ * migrates, all its activity on its old cpu [c0] happens-before any subsequent
+ * execution on its new cpu [c1].
+ *
+ * For migration (of runnable tasks) this is provided by the following means:
+ *
+ * A) UNLOCK of the rq(c0)->lock scheduling out task t
+ * B) migration for t is required to synchronize *both* rq(c0)->lock and
+ * rq(c1)->lock (if not at the same time, then in that order).
+ * C) LOCK of the rq(c1)->lock scheduling in task
+ *
+ * Transitivity guarantees that B happens after A and C after B.
+ * Note: we only require RCpc transitivity.
+ * Note: the cpu doing B need not be c0 or c1
+ *
+ * Example:
+ *
+ * CPU0 CPU1 CPU2
+ *
+ * LOCK rq(0)->lock
+ * sched-out X
+ * sched-in Y
+ * UNLOCK rq(0)->lock
+ *
+ * LOCK rq(0)->lock // orders against CPU0
+ * dequeue X
+ * UNLOCK rq(0)->lock
+ *
+ * LOCK rq(1)->lock
+ * enqueue X
+ * UNLOCK rq(1)->lock
+ *
+ * LOCK rq(1)->lock // orders against CPU2
+ * sched-out Z
+ * sched-in X
+ * UNLOCK rq(1)->lock
+ *
+ *
+ * BLOCKING -- aka. SLEEP + WAKEUP
+ *
+ * For blocking we (obviously) need to provide the same guarantee as for
+ * migration. However the means are completely different as there is no lock
+ * chain to provide order. Instead we do:
+ *
+ * 1) smp_store_release(X->on_cpu, 0)
+ * 2) smp_cond_acquire(!X->on_cpu)
+ *
+ * Example:
+ *
+ * CPU0 (schedule) CPU1 (try_to_wake_up) CPU2 (schedule)
+ *
+ * LOCK rq(0)->lock LOCK X->pi_lock
+ * dequeue X
+ * sched-out X
+ * smp_store_release(X->on_cpu, 0);
+ *
+ * smp_cond_acquire(!X->on_cpu);
+ * X->state = WAKING
+ * set_task_cpu(X,2)
+ *
+ * LOCK rq(2)->lock
+ * enqueue X
+ * X->state = RUNNING
+ * UNLOCK rq(2)->lock
+ *
+ * LOCK rq(2)->lock // orders against CPU1
+ * sched-out Z
+ * sched-in X
+ * UNLOCK rq(2)->lock
+ *
+ * UNLOCK X->pi_lock
+ * UNLOCK rq(0)->lock
+ *
+ *
+ * However; for wakeups there is a second guarantee we must provide, namely we
+ * must observe the state that lead to our wakeup. That is, not only must our
+ * task observe its own prior state, it must also observe the stores prior to
+ * its wakeup.
+ *
+ * This means that any means of doing remote wakeups must order the CPU doing
+ * the wakeup against the CPU the task is going to end up running on. This,
+ * however, is already required for the regular Program-Order guarantee above,
+ * since the waking CPU is the one issueing the ACQUIRE (smp_cond_acquire).
+ *
+ */
+
/**
* try_to_wake_up - wake up a thread
* @p: the thread to be awakened
#ifdef CONFIG_SMP
/*
- * If the owning (remote) cpu is still in the middle of schedule() with
- * this task as prev, wait until its done referencing the task.
+ * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
+ * possible to, falsely, observe p->on_cpu == 0.
+ *
+ * One must be running (->on_cpu == 1) in order to remove oneself
+ * from the runqueue.
+ *
+ * [S] ->on_cpu = 1; [L] ->on_rq
+ * UNLOCK rq->lock
+ * RMB
+ * LOCK rq->lock
+ * [S] ->on_rq = 0; [L] ->on_cpu
+ *
+ * Pairs with the full barrier implied in the UNLOCK+LOCK on rq->lock
+ * from the consecutive calls to schedule(); the first switching to our
+ * task, the second putting it to sleep.
*/
- while (p->on_cpu)
- cpu_relax();
+ smp_rmb();
+
/*
- * Pairs with the smp_wmb() in finish_lock_switch().
+ * If the owning (remote) cpu is still in the middle of schedule() with
+ * this task as prev, wait until its done referencing the task.
+ *
+ * Pairs with the smp_store_release() in finish_lock_switch().
+ *
+ * This ensures that tasks getting woken will be fully ordered against
+ * their previous state and preserve Program Order.
*/
- smp_rmb();
+ smp_cond_acquire(!p->on_cpu);
p->sched_contributes_to_load = !!task_contributes_to_load(p);
p->state = TASK_WAKING;
*/
int wake_up_process(struct task_struct *p)
{
- WARN_ON(task_is_stopped_or_traced(p));
return try_to_wake_up(p, TASK_NORMAL, 0);
}
EXPORT_SYMBOL(wake_up_process);
p->se.vruntime = 0;
INIT_LIST_HEAD(&p->se.group_node);
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ p->se.cfs_rq = NULL;
+#endif
+
#ifdef CONFIG_SCHEDSTATS
memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif
cpu = smp_processor_id();
rq = cpu_rq(cpu);
- rcu_note_context_switch();
prev = rq->curr;
/*
if (sched_feat(HRTICK))
hrtick_clear(rq);
+ local_irq_disable();
+ rcu_note_context_switch();
+
/*
* Make sure that signal_pending_state()->signal_pending() below
* can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
* done by the caller to avoid the race with signal_wake_up().
*/
smp_mb__before_spinlock();
- raw_spin_lock_irq(&rq->lock);
+ raw_spin_lock(&rq->lock);
lockdep_pin_lock(&rq->lock);
rq->clock_skip_update <<= 1; /* promote REQ to ACT */
{
memset(rd, 0, sizeof(*rd));
- if (!alloc_cpumask_var(&rd->span, GFP_KERNEL))
+ if (!zalloc_cpumask_var(&rd->span, GFP_KERNEL))
goto out;
- if (!alloc_cpumask_var(&rd->online, GFP_KERNEL))
+ if (!zalloc_cpumask_var(&rd->online, GFP_KERNEL))
goto free_span;
- if (!alloc_cpumask_var(&rd->dlo_mask, GFP_KERNEL))
+ if (!zalloc_cpumask_var(&rd->dlo_mask, GFP_KERNEL))
goto free_online;
- if (!alloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
+ if (!zalloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
goto free_dlo_mask;
init_dl_bw(&rd->dl_bw);
*/
struct task_group root_task_group;
LIST_HEAD(task_groups);
+
+/* Cacheline aligned slab cache for task_group */
+static struct kmem_cache *task_group_cache __read_mostly;
#endif
DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
#endif /* CONFIG_RT_GROUP_SCHED */
#ifdef CONFIG_CGROUP_SCHED
+ task_group_cache = KMEM_CACHE(task_group, 0);
+
list_add(&root_task_group.list, &task_groups);
INIT_LIST_HEAD(&root_task_group.children);
INIT_LIST_HEAD(&root_task_group.siblings);
autogroup_init(&init_task);
-
#endif /* CONFIG_CGROUP_SCHED */
for_each_possible_cpu(i) {
free_fair_sched_group(tg);
free_rt_sched_group(tg);
autogroup_free(tg);
- kfree(tg);
+ kmem_cache_free(task_group_cache, tg);
}
/* allocate runqueue etc for a new task group */
{
struct task_group *tg;
- tg = kzalloc(sizeof(*tg), GFP_KERNEL);
+ tg = kmem_cache_alloc(task_group_cache, GFP_KERNEL | __GFP_ZERO);
if (!tg)
return ERR_PTR(-ENOMEM);
pr_info("Task dump for CPU %d:\n", cpu);
sched_show_task(cpu_curr(cpu));
}
+
+/*
+ * Nice levels are multiplicative, with a gentle 10% change for every
+ * nice level changed. I.e. when a CPU-bound task goes from nice 0 to
+ * nice 1, it will get ~10% less CPU time than another CPU-bound task
+ * that remained on nice 0.
+ *
+ * The "10% effect" is relative and cumulative: from _any_ nice level,
+ * if you go up 1 level, it's -10% CPU usage, if you go down 1 level
+ * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25.
+ * If a task goes up by ~10% and another task goes down by ~10% then
+ * the relative distance between them is ~25%.)
+ */
+const int sched_prio_to_weight[40] = {
+ /* -20 */ 88761, 71755, 56483, 46273, 36291,
+ /* -15 */ 29154, 23254, 18705, 14949, 11916,
+ /* -10 */ 9548, 7620, 6100, 4904, 3906,
+ /* -5 */ 3121, 2501, 1991, 1586, 1277,
+ /* 0 */ 1024, 820, 655, 526, 423,
+ /* 5 */ 335, 272, 215, 172, 137,
+ /* 10 */ 110, 87, 70, 56, 45,
+ /* 15 */ 36, 29, 23, 18, 15,
+};
+
+/*
+ * Inverse (2^32/x) values of the sched_prio_to_weight[] array, precalculated.
+ *
+ * In cases where the weight does not change often, we can use the
+ * precalculated inverse to speed up arithmetics by turning divisions
+ * into multiplications:
+ */
+const u32 sched_prio_to_wmult[40] = {
+ /* -20 */ 48388, 59856, 76040, 92818, 118348,
+ /* -15 */ 147320, 184698, 229616, 287308, 360437,
+ /* -10 */ 449829, 563644, 704093, 875809, 1099582,
+ /* -5 */ 1376151, 1717300, 2157191, 2708050, 3363326,
+ /* 0 */ 4194304, 5237765, 6557202, 8165337, 10153587,
+ /* 5 */ 12820798, 15790321, 19976592, 24970740, 31350126,
+ /* 10 */ 39045157, 49367440, 61356676, 76695844, 95443717,
+ /* 15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
+};
projects / cascardo / linux.git / blobdiff