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rcu: priority boosting for TREE_PREEMPT_RCU 

Add priority boosting for TREE_PREEMPT_RCU, similar to that for
TINY_PREEMPT_RCU.  This is enabled by the default-off RCU_BOOST
kernel parameter.  The priority to which to boost preempted
RCU readers is controlled by the RCU_BOOST_PRIO kernel parameter
(defaulting to real-time priority 1) and the time to wait before
boosting the readers who are blocking a given grace period is
controlled by the RCU_BOOST_DELAY kernel parameter (defaulting to
500 milliseconds).

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2011-02-07 12:47:15 -08:00 committed by Paul E. McKenney
parent a26ac2455f
commit 27f4d28057
4 changed files with 411 additions and 51 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
init/Kconfig
View File

@ -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

115
kernel/rcutree.c
View File

@ -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;
@ -1435,25 +1450,34 @@ static void invoke_rcu_kthread(void)
local_irq_restore(flags);
}
/*
* 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) {

31
kernel/rcutree.h
View File

@ -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 */

314
kernel/rcutree_plugin.h
View File

@ -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;
}