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rcu: Define RCU-bh update API in terms of RCU

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Now that the main RCU API knows about softirq disabling and softirq's
quiescent states, the RCU-bh update code can be dispensed with.
This commit therefore removes the RCU-bh update-side implementation and
defines RCU-bh's update-side API in terms of that of either RCU-preempt or
RCU-sched, depending on the setting of the CONFIG_PREEMPT Kconfig option.

In kernels built with CONFIG_RCU_NOCB_CPU=y this has the knock-on effect
of reducing by one the number of rcuo kthreads per CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-07-01 07:40:52 -07:00
parent ba1c64c272
commit 65cfe3583b
7 changed files with 48 additions and 194 deletions
Download patch file Download diff file Expand all files Collapse all files

115
kernel/rcu/tiny.c
View file

@ -51,64 +51,22 @@ static struct rcu_ctrlblk rcu_sched_ctrlblk = {
.curtail = &rcu_sched_ctrlblk.rcucblist,
};
static struct rcu_ctrlblk rcu_bh_ctrlblk = {
.donetail = &rcu_bh_ctrlblk.rcucblist,
.curtail = &rcu_bh_ctrlblk.rcucblist,
};
void rcu_barrier_bh(void)
{
wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL(rcu_barrier_bh);
void rcu_barrier_sched(void)
{
wait_rcu_gp(call_rcu_sched);
}
EXPORT_SYMBOL(rcu_barrier_sched);
/*
* Helper function for rcu_sched_qs() and rcu_bh_qs().
* Also irqs are disabled to avoid confusion due to interrupt handlers
* invoking call_rcu().
*/
static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
{
if (rcp->donetail != rcp->curtail) {
rcp->donetail = rcp->curtail;
return 1;
}
return 0;
}
/*
* Record an rcu quiescent state. And an rcu_bh quiescent state while we
* are at it, given that any rcu quiescent state is also an rcu_bh
* quiescent state. Use "+" instead of "||" to defeat short circuiting.
*/
/* Record an rcu quiescent state. */
void rcu_sched_qs(void)
{
unsigned long flags;
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
rcu_qsctr_help(&rcu_bh_ctrlblk))
raise_softirq(RCU_SOFTIRQ);
local_irq_restore(flags);
}
/*
* Record an rcu_bh quiescent state.
*/
void rcu_bh_qs(void)
{
unsigned long flags;
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
if (rcu_sched_ctrlblk.donetail != rcu_sched_ctrlblk.curtail) {
rcu_sched_ctrlblk.donetail = rcu_sched_ctrlblk.curtail;
raise_softirq(RCU_SOFTIRQ);
}
local_irq_restore(flags);
}
@ -122,32 +80,27 @@ void rcu_check_callbacks(int user)
{
if (user)
rcu_sched_qs();
if (user || !in_softirq())
rcu_bh_qs();
}
/*
* Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
* whose grace period has elapsed.
*/
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* Invoke the RCU callbacks whose grace period has elapsed. */
static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
{
struct rcu_head *next, *list;
unsigned long flags;
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
if (rcp->donetail == &rcp->rcucblist) {
if (rcu_sched_ctrlblk.donetail == &rcu_sched_ctrlblk.rcucblist) {
/* No callbacks ready, so just leave. */
local_irq_restore(flags);
return;
}
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;
if (rcp->curtail == rcp->donetail)
rcp->curtail = &rcp->rcucblist;
rcp->donetail = &rcp->rcucblist;
list = rcu_sched_ctrlblk.rcucblist;
rcu_sched_ctrlblk.rcucblist = *rcu_sched_ctrlblk.donetail;
*rcu_sched_ctrlblk.donetail = NULL;
if (rcu_sched_ctrlblk.curtail == rcu_sched_ctrlblk.donetail)
rcu_sched_ctrlblk.curtail = &rcu_sched_ctrlblk.rcucblist;
rcu_sched_ctrlblk.donetail = &rcu_sched_ctrlblk.rcucblist;
local_irq_restore(flags);
/* Invoke the callbacks on the local list. */
@ -162,19 +115,13 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
}
}
static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
{
__rcu_process_callbacks(&rcu_sched_ctrlblk);
__rcu_process_callbacks(&rcu_bh_ctrlblk);
}
/*
* Wait for a grace period to elapse. But it is illegal to invoke
* synchronize_sched() from within an RCU read-side critical section.
* Therefore, any legal call to synchronize_sched() is a quiescent
* state, and so on a UP system, synchronize_sched() need do nothing.
* Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
* benefits of doing might_sleep() to reduce latency.)
* (But Lai Jiangshan points out the benefits of doing might_sleep()
* to reduce latency.)
*
* Cool, huh? (Due to Josh Triplett.)
*/
@ -188,11 +135,11 @@ void synchronize_sched(void)
EXPORT_SYMBOL_GPL(synchronize_sched);
/*
* Helper function for call_rcu() and call_rcu_bh().
* Post an RCU callback to be invoked after the end of an RCU-sched grace
* period. But since we have but one CPU, that would be after any
* quiescent state.
*/
static void __call_rcu(struct rcu_head *head,
rcu_callback_t func,
struct rcu_ctrlblk *rcp)
void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
{
unsigned long flags;
@ -201,8 +148,8 @@ static void __call_rcu(struct rcu_head *head,
head->next = NULL;
local_irq_save(flags);
*rcp->curtail = head;
rcp->curtail = &head->next;
*rcu_sched_ctrlblk.curtail = head;
rcu_sched_ctrlblk.curtail = &head->next;
local_irq_restore(flags);
if (unlikely(is_idle_task(current))) {
@ -210,28 +157,8 @@ static void __call_rcu(struct rcu_head *head,
resched_cpu(0);
}
}
/*
* Post an RCU callback to be invoked after the end of an RCU-sched grace
* period. But since we have but one CPU, that would be after any
* quiescent state.
*/
void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, &rcu_sched_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);
/*
* Post an RCU bottom-half callback to be invoked after any subsequent
* quiescent state.
*/
void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, &rcu_bh_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
void __init rcu_init(void)
{
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);