From 65cfe3583b612a22e12fba9a7bbd2d37ca5ad941 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 1 Jul 2018 07:40:52 -0700 Subject: rcu: Define RCU-bh update API in terms of RCU 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 --- kernel/rcu/tiny.c | 115 ++++++++++-------------------------------------------- 1 file changed, 21 insertions(+), 94 deletions(-) (limited to 'kernel/rcu/tiny.c') diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index befc9321a89c..cadcf63c4889 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -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); -- cgit