diff options
| -rw-r--r-- | init/Kconfig | 2 | ||||
| -rw-r--r-- | kernel/rcutree.c | 115 | ||||
| -rw-r--r-- | kernel/rcutree.h | 31 | ||||
| -rw-r--r-- | kernel/rcutree_plugin.h | 314 |
4 files changed, 411 insertions, 51 deletions
diff --git a/init/Kconfig b/init/Kconfig index d886b1e..2d964fa 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -485,7 +485,7 @@ config TREE_RCU_TRACE config RCU_BOOST bool "Enable RCU priority boosting" - depends on RT_MUTEXES && TINY_PREEMPT_RCU + depends on RT_MUTEXES && PREEMPT_RCU default n help This option boosts the priority of preempted RCU readers that diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 18e3331..28fd92a 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -81,6 +81,8 @@ DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); +static struct rcu_state *rcu_state; + int rcu_scheduler_active __read_mostly; EXPORT_SYMBOL_GPL(rcu_scheduler_active); @@ -94,7 +96,7 @@ 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); +static void invoke_rcu_cpu_kthread(void); #define RCU_KTHREAD_PRIO 1 /* RT priority for per-CPU kthreads. */ @@ -791,6 +793,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) rnp->completed = rsp->completed; rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ rcu_start_gp_per_cpu(rsp, rnp, rdp); + rcu_preempt_boost_start_gp(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } @@ -826,6 +829,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) rnp->completed = rsp->completed; if (rnp == rdp->mynode) rcu_start_gp_per_cpu(rsp, rnp, rdp); + rcu_preempt_boost_start_gp(rnp); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } @@ -882,7 +886,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, return; } rnp->qsmask &= ~mask; - if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) { + if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { /* Other bits still set at this level, so done. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); @@ -1089,8 +1093,11 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) t = rnp->node_kthread_task; if (t != NULL && rnp->qsmaskinit == 0) { - kthread_stop(t); + raw_spin_lock_irqsave(&rnp->lock, flags); rnp->node_kthread_task = NULL; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + kthread_stop(t); + rcu_stop_boost_kthread(rnp); } else rcu_node_kthread_setaffinity(rnp); } @@ -1190,7 +1197,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) /* Re-raise the RCU softirq if there are callbacks remaining. */ if (cpu_has_callbacks_ready_to_invoke(rdp)) - invoke_rcu_kthread(); + invoke_rcu_cpu_kthread(); } /* @@ -1236,7 +1243,7 @@ void rcu_check_callbacks(int cpu, int user) } rcu_preempt_check_callbacks(cpu); if (rcu_pending(cpu)) - invoke_rcu_kthread(); + invoke_rcu_cpu_kthread(); } #ifdef CONFIG_SMP @@ -1244,6 +1251,8 @@ void rcu_check_callbacks(int cpu, int user) /* * Scan the leaf rcu_node structures, processing dyntick state for any that * have not yet encountered a quiescent state, using the function specified. + * Also initiate boosting for any threads blocked on the root rcu_node. + * * The caller must have suppressed start of new grace periods. */ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) @@ -1262,6 +1271,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) return; } if (rnp->qsmask == 0) { + rcu_initiate_boost(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); continue; } @@ -1280,6 +1290,11 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) } raw_spin_unlock_irqrestore(&rnp->lock, flags); } + rnp = rcu_get_root(rsp); + raw_spin_lock_irqsave(&rnp->lock, flags); + if (rnp->qsmask == 0) + rcu_initiate_boost(rnp); + raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* @@ -1417,7 +1432,7 @@ static void rcu_process_callbacks(void) * the current CPU with interrupts disabled, the rcu_cpu_kthread_task * cannot disappear out from under us. */ -static void invoke_rcu_kthread(void) +static void invoke_rcu_cpu_kthread(void) { unsigned long flags; wait_queue_head_t *q; @@ -1436,24 +1451,33 @@ static void invoke_rcu_kthread(void) } /* + * Wake up the specified per-rcu_node-structure kthread. + * The caller must hold ->lock. + */ +static void invoke_rcu_node_kthread(struct rcu_node *rnp) +{ + struct task_struct *t; + + t = rnp->node_kthread_task; + if (t != NULL) + wake_up_process(t); +} + +/* * Timer handler to initiate the waking up of per-CPU kthreads that * have yielded the CPU due to excess numbers of RCU callbacks. + * We wake up the per-rcu_node kthread, which in turn will wake up + * the booster kthread. */ static void rcu_cpu_kthread_timer(unsigned long arg) { unsigned long flags; - struct rcu_data *rdp = (struct rcu_data *)arg; + struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, 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); + invoke_rcu_node_kthread(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); } @@ -1463,13 +1487,12 @@ static void rcu_cpu_kthread_timer(unsigned long arg) * remain preempted. Either way, we restore our real-time priority * before returning. */ -static void rcu_yield(int cpu) +static void rcu_yield(void (*f)(unsigned long), unsigned long arg) { - 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); + setup_timer_on_stack(&yield_timer, f, arg); mod_timer(&yield_timer, jiffies + 2); sp.sched_priority = 0; sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); @@ -1540,7 +1563,7 @@ static int rcu_cpu_kthread(void *arg) else spincnt = 0; if (spincnt > 10) { - rcu_yield(cpu); + rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu); spincnt = 0; } } @@ -1597,6 +1620,7 @@ static int rcu_node_kthread(void *arg) raw_spin_lock_irqsave(&rnp->lock, flags); mask = rnp->wakemask; rnp->wakemask = 0; + rcu_initiate_boost(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) { if ((mask & 0x1) == 0) @@ -1618,7 +1642,8 @@ static int rcu_node_kthread(void *arg) /* * Set the per-rcu_node kthread's affinity to cover all CPUs that are - * served by the rcu_node in question. + * served by the rcu_node in question. The CPU hotplug lock is still + * held, so the value of rnp->qsmaskinit will be stable. */ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp) { @@ -1626,8 +1651,7 @@ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp) int cpu; unsigned long mask = rnp->qsmaskinit; - if (rnp->node_kthread_task == NULL || - rnp->qsmaskinit == 0) + if (rnp->node_kthread_task == NULL || mask == 0) return; if (!alloc_cpumask_var(&cm, GFP_KERNEL)) return; @@ -1636,31 +1660,40 @@ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp) if (mask & 0x1) cpumask_set_cpu(cpu, cm); set_cpus_allowed_ptr(rnp->node_kthread_task, cm); + rcu_boost_kthread_setaffinity(rnp, cm); free_cpumask_var(cm); } /* * Spawn a per-rcu_node kthread, setting priority and affinity. + * Called during boot before online/offline can happen, or, if + * during runtime, with the main CPU-hotplug locks held. So only + * one of these can be executing at a time. */ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, struct rcu_node *rnp) { + unsigned long flags; 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) + rnp->qsmaskinit == 0) 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; + if (rnp->node_kthread_task == NULL) { + t = kthread_create(rcu_node_kthread, (void *)rnp, + "rcun%d", rnp_index); + if (IS_ERR(t)) + return PTR_ERR(t); + raw_spin_lock_irqsave(&rnp->lock, flags); + rnp->node_kthread_task = t; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + wake_up_process(t); + sp.sched_priority = 99; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + } + return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index); } /* @@ -1678,10 +1711,16 @@ static int __init rcu_spawn_kthreads(void) 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); - } + rnp = rcu_get_root(rcu_state); + init_waitqueue_head(&rnp->node_wq); + rcu_init_boost_waitqueue(rnp); + (void)rcu_spawn_one_node_kthread(rcu_state, rnp); + if (NUM_RCU_NODES > 1) + rcu_for_each_leaf_node(rcu_state, rnp) { + init_waitqueue_head(&rnp->node_wq); + rcu_init_boost_waitqueue(rnp); + (void)rcu_spawn_one_node_kthread(rcu_state, rnp); + } return 0; } early_initcall(rcu_spawn_kthreads); @@ -2087,14 +2126,14 @@ static void __cpuinit rcu_online_cpu(int cpu) static void __cpuinit rcu_online_kthreads(int cpu) { - struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu); + struct rcu_data *rdp = per_cpu_ptr(rcu_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); + (void)rcu_spawn_one_node_kthread(rcu_state, rnp); } } @@ -2105,7 +2144,7 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { long cpu = (long)hcpu; - struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu); + struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); struct rcu_node *rnp = rdp->mynode; switch (action) { diff --git a/kernel/rcutree.h b/kernel/rcutree.h index c021380..8db0cdc 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -135,6 +135,24 @@ struct rcu_node { /* if there is no such task. If there */ /* is no current expedited grace period, */ /* then there can cannot be any such task. */ +#ifdef CONFIG_RCU_BOOST + struct list_head *boost_tasks; + /* Pointer to first task that needs to be */ + /* priority boosted, or NULL if no priority */ + /* boosting is needed for this rcu_node */ + /* structure. If there are no tasks */ + /* queued on this rcu_node structure that */ + /* are blocking the current grace period, */ + /* there can be no such task. */ + unsigned long boost_time; + /* When to start boosting (jiffies). */ + struct task_struct *boost_kthread_task; + /* kthread that takes care of priority */ + /* boosting for this rcu_node structure. */ + wait_queue_head_t boost_wq; + /* Wait queue on which to park the boost */ + /* kthread. */ +#endif /* #ifdef CONFIG_RCU_BOOST */ struct task_struct *node_kthread_task; /* kthread that takes care of this rcu_node */ /* structure, for example, awakening the */ @@ -365,7 +383,7 @@ DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data); static void rcu_bootup_announce(void); long rcu_batches_completed(void); static void rcu_preempt_note_context_switch(int cpu); -static int rcu_preempted_readers(struct rcu_node *rnp); +static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); #ifdef CONFIG_HOTPLUG_CPU static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags); @@ -392,5 +410,16 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu); static void rcu_preempt_send_cbs_to_online(void); static void __init __rcu_init_preempt(void); static void rcu_needs_cpu_flush(void); +static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp); +static void rcu_initiate_boost(struct rcu_node *rnp); +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, + cpumask_var_t cm); +static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); +static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, + struct rcu_node *rnp, + int rnp_index); +#ifdef CONFIG_HOTPLUG_CPU +static void rcu_stop_boost_kthread(struct rcu_node *rnp); +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ #endif /* #ifndef RCU_TREE_NONCORE */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index b9bd69a..5964f82 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -66,6 +66,7 @@ static void __init rcu_bootup_announce_oddness(void) struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); +static struct rcu_state *rcu_state = &rcu_preempt_state; static int rcu_preempted_readers_exp(struct rcu_node *rnp); @@ -179,6 +180,10 @@ static void rcu_preempt_note_context_switch(int cpu) if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); rnp->gp_tasks = &t->rcu_node_entry; +#ifdef CONFIG_RCU_BOOST + if (rnp->boost_tasks != NULL) + rnp->boost_tasks = rnp->gp_tasks; +#endif /* #ifdef CONFIG_RCU_BOOST */ } else { list_add(&t->rcu_node_entry, &rnp->blkd_tasks); if (rnp->qsmask & rdp->grpmask) @@ -218,7 +223,7 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock); * for the specified rcu_node structure. If the caller needs a reliable * answer, it must hold the rcu_node's ->lock. */ -static int rcu_preempted_readers(struct rcu_node *rnp) +static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) { return rnp->gp_tasks != NULL; } @@ -236,7 +241,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) unsigned long mask; struct rcu_node *rnp_p; - if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) { + if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; /* Still need more quiescent states! */ } @@ -325,7 +330,7 @@ static void rcu_read_unlock_special(struct task_struct *t) break; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } - empty = !rcu_preempted_readers(rnp); + empty = !rcu_preempt_blocked_readers_cgp(rnp); empty_exp = !rcu_preempted_readers_exp(rnp); smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ np = rcu_next_node_entry(t, rnp); @@ -334,6 +339,10 @@ static void rcu_read_unlock_special(struct task_struct *t) rnp->gp_tasks = np; if (&t->rcu_node_entry == rnp->exp_tasks) rnp->exp_tasks = np; +#ifdef CONFIG_RCU_BOOST + if (&t->rcu_node_entry == rnp->boost_tasks) + rnp->boost_tasks = np; +#endif /* #ifdef CONFIG_RCU_BOOST */ t->rcu_blocked_node = NULL; /* @@ -346,6 +355,15 @@ static void rcu_read_unlock_special(struct task_struct *t) else rcu_report_unblock_qs_rnp(rnp, flags); +#ifdef CONFIG_RCU_BOOST + /* Unboost if we were boosted. */ + if (special & RCU_READ_UNLOCK_BOOSTED) { + t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; + rt_mutex_unlock(t->rcu_boost_mutex); + t->rcu_boost_mutex = NULL; + } +#endif /* #ifdef CONFIG_RCU_BOOST */ + /* * If this was the last task on the expedited lists, * then we need to report up the rcu_node hierarchy. @@ -391,7 +409,7 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) unsigned long flags; struct task_struct *t; - if (!rcu_preempted_readers(rnp)) + if (!rcu_preempt_blocked_readers_cgp(rnp)) return; raw_spin_lock_irqsave(&rnp->lock, flags); t = list_entry(rnp->gp_tasks, @@ -430,7 +448,7 @@ static void rcu_print_task_stall(struct rcu_node *rnp) { struct task_struct *t; - if (!rcu_preempted_readers(rnp)) + if (!rcu_preempt_blocked_readers_cgp(rnp)) return; t = list_entry(rnp->gp_tasks, struct task_struct, rcu_node_entry); @@ -460,7 +478,7 @@ static void rcu_preempt_stall_reset(void) */ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) { - WARN_ON_ONCE(rcu_preempted_readers(rnp)); + WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); if (!list_empty(&rnp->blkd_tasks)) rnp->gp_tasks = rnp->blkd_tasks.next; WARN_ON_ONCE(rnp->qsmask); @@ -509,7 +527,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, * absolutely necessary, but this is a good performance/complexity * tradeoff. */ - if (rcu_preempted_readers(rnp)) + if (rcu_preempt_blocked_readers_cgp(rnp)) retval |= RCU_OFL_TASKS_NORM_GP; if (rcu_preempted_readers_exp(rnp)) retval |= RCU_OFL_TASKS_EXP_GP; @@ -525,8 +543,22 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, rnp_root->gp_tasks = rnp->gp_tasks; if (&t->rcu_node_entry == rnp->exp_tasks) rnp_root->exp_tasks = rnp->exp_tasks; +#ifdef CONFIG_RCU_BOOST + if (&t->rcu_node_entry == rnp->boost_tasks) + rnp_root->boost_tasks = rnp->boost_tasks; +#endif /* #ifdef CONFIG_RCU_BOOST */ raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ } + +#ifdef CONFIG_RCU_BOOST + /* In case root is being boosted and leaf is not. */ + raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ + if (rnp_root->boost_tasks != NULL && + rnp_root->boost_tasks != rnp_root->gp_tasks) + rnp_root->boost_tasks = rnp_root->gp_tasks; + raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ +#endif /* #ifdef CONFIG_RCU_BOOST */ + rnp->gp_tasks = NULL; rnp->exp_tasks = NULL; return retval; @@ -684,6 +716,7 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) raw_spin_lock(&rnp->lock); /* irqs already disabled */ if (!list_empty(&rnp->blkd_tasks)) { rnp->exp_tasks = rnp->blkd_tasks.next; + rcu_initiate_boost(rnp); must_wait = 1; } raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ @@ -830,6 +863,8 @@ void exit_rcu(void) #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ +static struct rcu_state *rcu_state = &rcu_sched_state; + /* * Tell them what RCU they are running. */ @@ -870,7 +905,7 @@ static void rcu_preempt_note_context_switch(int cpu) * Because preemptable RCU does not exist, there are never any preempted * RCU readers. */ -static int rcu_preempted_readers(struct rcu_node *rnp) +static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) { return 0; } @@ -1034,6 +1069,263 @@ static void __init __rcu_init_preempt(void) #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ +#ifdef CONFIG_RCU_BOOST + +#include "rtmutex_common.h" + +/* + * Carry out RCU priority boosting on the task indicated by ->exp_tasks + * or ->boost_tasks, advancing the pointer to the next task in the + * ->blkd_tasks list. + * + * Note that irqs must be enabled: boosting the task can block. + * Returns 1 if there are more tasks needing to be boosted. + */ +static int rcu_boost(struct rcu_node *rnp) +{ + unsigned long flags; + struct rt_mutex mtx; + struct task_struct *t; + struct list_head *tb; + + if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) + return 0; /* Nothing left to boost. */ + + raw_spin_lock_irqsave(&rnp->lock, flags); + + /* + * Recheck under the lock: all tasks in need of boosting + * might exit their RCU read-side critical sections on their own. + */ + if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return 0; + } + + /* + * Preferentially boost tasks blocking expedited grace periods. + * This cannot starve the normal grace periods because a second + * expedited grace period must boost all blocked tasks, including + * those blocking the pre-existing normal grace period. + */ + if (rnp->exp_tasks != NULL) + tb = rnp->exp_tasks; + else + tb = rnp->boost_tasks; + + /* + * We boost task t by manufacturing an rt_mutex that appears to + * be held by task t. We leave a pointer to that rt_mutex where + * task t can find it, and task t will release the mutex when it + * exits its outermost RCU read-side critical section. Then + * simply acquiring this artificial rt_mutex will boost task + * t's priority. (Thanks to tglx for suggesting this approach!) + * + * Note that task t must acquire rnp->lock to remove itself from + * the ->blkd_tasks list, which it will do from exit() if from + * nowhere else. We therefore are guaranteed that task t will + * stay around at least until we drop rnp->lock. Note that + * rnp->lock also resolves races between our priority boosting + * and task t's exiting its outermost RCU read-side critical + * section. + */ + t = container_of(tb, struct task_struct, rcu_node_entry); + rt_mutex_init_proxy_locked(&mtx, t); + t->rcu_boost_mutex = &mtx; + t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ + rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ + + return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL; +} + +/* + * Timer handler to initiate waking up of boost kthreads that + * have yielded the CPU due to excessive numbers of tasks to + * boost. We wake up the per-rcu_node kthread, which in turn + * will wake up the booster kthread. + */ +static void rcu_boost_kthread_timer(unsigned long arg) +{ + unsigned long flags; + struct rcu_node *rnp = (struct rcu_node *)arg; + + raw_spin_lock_irqsave(&rnp->lock, flags); + invoke_rcu_node_kthread(rnp); + raw_spin_unlock_irqrestore(&rnp->lock, flags); +} + +/* + * Priority-boosting kthread. One per leaf rcu_node and one for the + * root rcu_node. + */ +static int rcu_boost_kthread(void *arg) +{ + struct rcu_node *rnp = (struct rcu_node *)arg; + int spincnt = 0; + int more2boost; + + for (;;) { + wait_event_interruptible(rnp->boost_wq, rnp->boost_tasks || + rnp->exp_tasks || + kthread_should_stop()); + if (kthread_should_stop()) + break; + more2boost = rcu_boost(rnp); + if (more2boost) + spincnt++; + else + spincnt = 0; + if (spincnt > 10) { + rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp); + spincnt = 0; + } + } + return 0; +} + +/* + * Check to see if it is time to start boosting RCU readers that are + * blocking the current grace period, and, if so, tell the per-rcu_node + * kthread to start boosting them. If there is an expedited grace + * period in progress, it is always time to boost. + * + * The caller must hold rnp->lock. + */ +static void rcu_initiate_boost(struct rcu_node *rnp) +{ + struct task_struct *t; + + if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) + return; + if (rnp->exp_tasks != NULL || + (rnp->gp_tasks != NULL && + rnp->boost_tasks == NULL && + rnp->qsmask == 0 && + ULONG_CMP_GE(jiffies, rnp->boost_time))) { + if (rnp->exp_tasks == NULL) + rnp->boost_tasks = rnp->gp_tasks; + t = rnp->boost_kthread_task; + if (t != NULL) + wake_up_process(t); + } +} + +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, + cpumask_var_t cm) +{ + unsigned long flags; + struct task_struct *t; + + raw_spin_lock_irqsave(&rnp->lock, flags); + t = rnp->boost_kthread_task; + if (t != NULL) + set_cpus_allowed_ptr(rnp->boost_kthread_task, cm); + raw_spin_unlock_irqrestore(&rnp->lock, flags); +} + +#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) + +/* + * Do priority-boost accounting for the start of a new grace period. + */ +static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) +{ + rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; +} + +/* + * Initialize the RCU-boost waitqueue. + */ +static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp) +{ + init_waitqueue_head(&rnp->boost_wq); +} + +/* + * Create an RCU-boost kthread for the specified node if one does not + * already exist. We only create this kthread for preemptible RCU. + * Returns zero if all is well, a negated errno otherwise. + */ +static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, + struct rcu_node *rnp, + int rnp_index) +{ + unsigned long flags; + struct sched_param sp; + struct task_struct *t; + + if (&rcu_preempt_state != rsp) + return 0; + if (rnp->boost_kthread_task != NULL) + return 0; + t = kthread_create(rcu_boost_kthread, (void *)rnp, + "rcub%d", rnp_index); + if (IS_ERR(t)) + return PTR_ERR(t); + raw_spin_lock_irqsave(&rnp->lock, flags); + rnp->boost_kthread_task = t; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + wake_up_process(t); + sp.sched_priority = RCU_KTHREAD_PRIO; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + return 0; +} + +#ifdef CONFIG_HOTPLUG_CPU + +static void rcu_stop_boost_kthread(struct rcu_node *rnp) +{ + unsigned long flags; + struct task_struct *t; + + raw_spin_lock_irqsave(&rnp->lock, flags); + t = rnp->boost_kthread_task; + rnp->boost_kthread_task = NULL; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (t != NULL) + kthread_stop(t); +} + +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ + +#else /* #ifdef CONFIG_RCU_BOOST */ + +static void rcu_initiate_boost(struct rcu_node *rnp) +{ +} + +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, + cpumask_var_t cm) +{ +} + +static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) +{ +} + +static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp) +{ +} + +static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, + struct rcu_node *rnp, + int rnp_index) +{ + return 0; +} + +#ifdef CONFIG_HOTPLUG_CPU + +static void rcu_stop_boost_kthread(struct rcu_node *rnp) +{ +} + +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ + +#endif /* #else #ifdef CONFIG_RCU_BOOST */ + #ifndef CONFIG_SMP void synchronize_sched_expedited(void) @@ -1206,8 +1498,8 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); * * Because it is not legal to invoke rcu_process_callbacks() with irqs * disabled, we do one pass of force_quiescent_state(), then do a - * invoke_rcu_kthread() to cause rcu_process_callbacks() to be invoked later. - * The per-cpu rcu_dyntick_drain variable controls the sequencing. + * invoke_rcu_cpu_kthread() to cause rcu_process_callbacks() to be invoked + * later. The per-cpu rcu_dyntick_drain variable controls the sequencing. */ int rcu_needs_cpu(int cpu) { @@ -1257,7 +1549,7 @@ int rcu_needs_cpu(int cpu) /* If RCU callbacks are still pending, RCU still needs this CPU. */ if (c) - invoke_rcu_kthread(); + invoke_rcu_cpu_kthread(); return c; } |
