#include <linux/mutex.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
+#include <linux/wait.h>
+#include <linux/kthread.h>
#include "rcutree.h"
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
+/*
+ * Control variables for per-CPU and per-rcu_node kthreads. These
+ * handle all flavors of RCU.
+ */
+static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
+static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
+static DEFINE_PER_CPU(char, rcu_cpu_has_work);
+static char rcu_kthreads_spawnable;
+
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp);
+static void invoke_rcu_kthread(void);
+
+#define RCU_KTHREAD_PRIO 1 /* RT priority for per-CPU kthreads. */
+
/*
* Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
* permit this function to be invoked without holding the root rcu_node
/*
* Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
* and move all callbacks from the outgoing CPU to the current one.
+ * There can only be one CPU hotplug operation at a time, so no other
+ * CPU can be attempting to update rcu_cpu_kthread_task.
*/
static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
{
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp;
+ struct task_struct *t;
+
+ /* Stop the CPU's kthread. */
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (t != NULL) {
+ per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
+ kthread_stop(t);
+ }
/* Exclude any attempts to start a new grace period. */
raw_spin_lock_irqsave(&rsp->onofflock, flags);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp);
+
+ /*
+ * If there are no more online CPUs for this rcu_node structure,
+ * kill the rcu_node structure's kthread. Otherwise, adjust its
+ * affinity.
+ */
+ t = rnp->node_kthread_task;
+ if (t != NULL &&
+ rnp->qsmaskinit == 0) {
+ kthread_stop(t);
+ rnp->node_kthread_task = NULL;
+ } else
+ rcu_node_kthread_setaffinity(rnp);
}
/*
/* Re-raise the RCU softirq if there are callbacks remaining. */
if (cpu_has_callbacks_ready_to_invoke(rdp))
- raise_softirq(RCU_SOFTIRQ);
+ invoke_rcu_kthread();
}
/*
}
rcu_preempt_check_callbacks(cpu);
if (rcu_pending(cpu))
- raise_softirq(RCU_SOFTIRQ);
+ invoke_rcu_kthread();
}
#ifdef CONFIG_SMP
/*
* Do softirq processing for the current CPU.
*/
-static void rcu_process_callbacks(struct softirq_action *unused)
+static void rcu_process_callbacks(void)
{
__rcu_process_callbacks(&rcu_sched_state,
&__get_cpu_var(rcu_sched_data));
rcu_needs_cpu_flush();
}
+/*
+ * Wake up the current CPU's kthread. This replaces raise_softirq()
+ * in earlier versions of RCU. Note that because we are running on
+ * the current CPU with interrupts disabled, the rcu_cpu_kthread_task
+ * cannot disappear out from under us.
+ */
+static void invoke_rcu_kthread(void)
+{
+ unsigned long flags;
+ wait_queue_head_t *q;
+ int cpu;
+
+ local_irq_save(flags);
+ cpu = smp_processor_id();
+ per_cpu(rcu_cpu_has_work, cpu) = 1;
+ if (per_cpu(rcu_cpu_kthread_task, cpu) == NULL) {
+ local_irq_restore(flags);
+ return;
+ }
+ q = &per_cpu(rcu_cpu_wq, cpu);
+ wake_up(q);
+ local_irq_restore(flags);
+}
+
+/*
+ * Timer handler to initiate the waking up of per-CPU kthreads that
+ * have yielded the CPU due to excess numbers of RCU callbacks.
+ */
+static void rcu_cpu_kthread_timer(unsigned long arg)
+{
+ unsigned long flags;
+ struct rcu_data *rdp = (struct rcu_data *)arg;
+ struct rcu_node *rnp = rdp->mynode;
+ struct task_struct *t;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ rnp->wakemask |= rdp->grpmask;
+ t = rnp->node_kthread_task;
+ if (t == NULL) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return;
+ }
+ wake_up_process(t);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Drop to non-real-time priority and yield, but only after posting a
+ * timer that will cause us to regain our real-time priority if we
+ * remain preempted. Either way, we restore our real-time priority
+ * before returning.
+ */
+static void rcu_yield(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
+ struct sched_param sp;
+ struct timer_list yield_timer;
+
+ setup_timer_on_stack(&yield_timer, rcu_cpu_kthread_timer, (unsigned long)rdp);
+ mod_timer(&yield_timer, jiffies + 2);
+ sp.sched_priority = 0;
+ sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
+ schedule();
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+ del_timer(&yield_timer);
+}
+
+/*
+ * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
+ * This can happen while the corresponding CPU is either coming online
+ * or going offline. We cannot wait until the CPU is fully online
+ * before starting the kthread, because the various notifier functions
+ * can wait for RCU grace periods. So we park rcu_cpu_kthread() until
+ * the corresponding CPU is online.
+ *
+ * Return 1 if the kthread needs to stop, 0 otherwise.
+ *
+ * Caller must disable bh. This function can momentarily enable it.
+ */
+static int rcu_cpu_kthread_should_stop(int cpu)
+{
+ while (cpu_is_offline(cpu) ||
+ !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) ||
+ smp_processor_id() != cpu) {
+ if (kthread_should_stop())
+ return 1;
+ local_bh_enable();
+ schedule_timeout_uninterruptible(1);
+ if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)))
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
+ local_bh_disable();
+ }
+ return 0;
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
+ * earlier RCU softirq.
+ */
+static int rcu_cpu_kthread(void *arg)
+{
+ int cpu = (int)(long)arg;
+ unsigned long flags;
+ int spincnt = 0;
+ wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
+ char work;
+ char *workp = &per_cpu(rcu_cpu_has_work, cpu);
+
+ for (;;) {
+ wait_event_interruptible(*wqp,
+ *workp != 0 || kthread_should_stop());
+ local_bh_disable();
+ if (rcu_cpu_kthread_should_stop(cpu)) {
+ local_bh_enable();
+ break;
+ }
+ local_irq_save(flags);
+ work = *workp;
+ *workp = 0;
+ local_irq_restore(flags);
+ if (work)
+ rcu_process_callbacks();
+ local_bh_enable();
+ if (*workp != 0)
+ spincnt++;
+ else
+ spincnt = 0;
+ if (spincnt > 10) {
+ rcu_yield(cpu);
+ spincnt = 0;
+ }
+ }
+ return 0;
+}
+
+/*
+ * Spawn a per-CPU kthread, setting up affinity and priority.
+ * Because the CPU hotplug lock is held, no other CPU will be attempting
+ * to manipulate rcu_cpu_kthread_task. There might be another CPU
+ * attempting to access it during boot, but the locking in kthread_bind()
+ * will enforce sufficient ordering.
+ */
+static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
+{
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (!rcu_kthreads_spawnable ||
+ per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
+ return 0;
+ t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ kthread_bind(t, cpu);
+ WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
+ per_cpu(rcu_cpu_kthread_task, cpu) = t;
+ wake_up_process(t);
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ return 0;
+}
+
+/*
+ * Per-rcu_node kthread, which is in charge of waking up the per-CPU
+ * kthreads when needed. We ignore requests to wake up kthreads
+ * for offline CPUs, which is OK because force_quiescent_state()
+ * takes care of this case.
+ */
+static int rcu_node_kthread(void *arg)
+{
+ int cpu;
+ unsigned long flags;
+ unsigned long mask;
+ struct rcu_node *rnp = (struct rcu_node *)arg;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ for (;;) {
+ wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
+ kthread_should_stop());
+ if (kthread_should_stop())
+ break;
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ mask = rnp->wakemask;
+ rnp->wakemask = 0;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
+ if ((mask & 0x1) == 0)
+ continue;
+ preempt_disable();
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (!cpu_online(cpu) || t == NULL) {
+ preempt_enable();
+ continue;
+ }
+ per_cpu(rcu_cpu_has_work, cpu) = 1;
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ preempt_enable();
+ }
+ }
+ return 0;
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question.
+ */
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp)
+{
+ cpumask_var_t cm;
+ int cpu;
+ unsigned long mask = rnp->qsmaskinit;
+
+ if (rnp->node_kthread_task == NULL ||
+ rnp->qsmaskinit == 0)
+ return;
+ if (!alloc_cpumask_var(&cm, GFP_KERNEL))
+ return;
+ cpumask_clear(cm);
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
+ if (mask & 0x1)
+ cpumask_set_cpu(cpu, cm);
+ set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
+ free_cpumask_var(cm);
+}
+
+/*
+ * Spawn a per-rcu_node kthread, setting priority and affinity.
+ */
+static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
+ struct rcu_node *rnp)
+{
+ int rnp_index = rnp - &rsp->node[0];
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (!rcu_kthreads_spawnable ||
+ rnp->qsmaskinit == 0 ||
+ rnp->node_kthread_task != NULL)
+ return 0;
+ t = kthread_create(rcu_node_kthread, (void *)rnp, "rcun%d", rnp_index);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ rnp->node_kthread_task = t;
+ wake_up_process(t);
+ sp.sched_priority = 99;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ return 0;
+}
+
+/*
+ * Spawn all kthreads -- called as soon as the scheduler is running.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+ int cpu;
+ struct rcu_node *rnp;
+
+ rcu_kthreads_spawnable = 1;
+ for_each_possible_cpu(cpu) {
+ init_waitqueue_head(&per_cpu(rcu_cpu_wq, cpu));
+ per_cpu(rcu_cpu_has_work, cpu) = 0;
+ if (cpu_online(cpu))
+ (void)rcu_spawn_one_cpu_kthread(cpu);
+ }
+ rcu_for_each_leaf_node(&rcu_sched_state, rnp) {
+ init_waitqueue_head(&rnp->node_wq);
+ (void)rcu_spawn_one_node_kthread(&rcu_sched_state, rnp);
+ }
+ return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp)
rcu_preempt_init_percpu_data(cpu);
}
+static void __cpuinit rcu_online_kthreads(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
+ struct rcu_node *rnp = rdp->mynode;
+
+ /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+ if (rcu_kthreads_spawnable) {
+ (void)rcu_spawn_one_cpu_kthread(cpu);
+ if (rnp->node_kthread_task == NULL)
+ (void)rcu_spawn_one_node_kthread(&rcu_sched_state, rnp);
+ }
+}
+
/*
* Handle CPU online/offline notification events.
*/
unsigned long action, void *hcpu)
{
long cpu = (long)hcpu;
+ struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
+ struct rcu_node *rnp = rdp->mynode;
switch (action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
rcu_online_cpu(cpu);
+ rcu_online_kthreads(cpu);
+ break;
+ case CPU_ONLINE:
+ rcu_node_kthread_setaffinity(rnp);
break;
case CPU_DYING:
case CPU_DYING_FROZEN:
rcu_init_one(&rcu_sched_state, &rcu_sched_data);
rcu_init_one(&rcu_bh_state, &rcu_bh_data);
__rcu_init_preempt();
- open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
/*
* We don't need protection against CPU-hotplug here because
projects / users / hch / misc.git / commitdiff