From 616c310e83b872024271c915c1b9ab505b9efad9 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 27 Mar 2012 16:02:08 -0700 Subject: rcu: Move PREEMPT_RCU preemption to switch_to() invocation Currently, PREEMPT_RCU readers are enqueued upon entry to the scheduler. This is inefficient because enqueuing is required only if there is a context switch, and entry to the scheduler does not guarantee a context switch. The commit therefore moves the enqueuing to immediately precede the call to switch_to() from the scheduler. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Linus Torvalds --- include/linux/rcutiny.h | 6 ------ 1 file changed, 6 deletions(-) (limited to 'include/linux/rcutiny.h') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index e93df77176d..080b5bdda28 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -87,10 +87,6 @@ static inline void kfree_call_rcu(struct rcu_head *head, #ifdef CONFIG_TINY_RCU -static inline void rcu_preempt_note_context_switch(void) -{ -} - static inline void exit_rcu(void) { } @@ -102,7 +98,6 @@ static inline int rcu_needs_cpu(int cpu) #else /* #ifdef CONFIG_TINY_RCU */ -void rcu_preempt_note_context_switch(void); extern void exit_rcu(void); int rcu_preempt_needs_cpu(void); @@ -116,7 +111,6 @@ static inline int rcu_needs_cpu(int cpu) static inline void rcu_note_context_switch(int cpu) { rcu_sched_qs(cpu); - rcu_preempt_note_context_switch(); } /* -- cgit v1.2.3-70-g09d2 From 9dd8fb16c36178df2066387d2abd44d8b4dca8c8 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 13 Apr 2012 12:54:22 -0700 Subject: rcu: Make exit_rcu() more precise and consolidate When running preemptible RCU, if a task exits in an RCU read-side critical section having blocked within that same RCU read-side critical section, the task must be removed from the list of tasks blocking a grace period (perhaps the current grace period, perhaps the next grace period, depending on timing). The exit() path invokes exit_rcu() to do this cleanup. However, the current implementation of exit_rcu() needlessly does the cleanup even if the task did not block within the current RCU read-side critical section, which wastes time and needlessly increases the size of the state space. Fix this by only doing the cleanup if the current task is actually on the list of tasks blocking some grace period. While we are at it, consolidate the two identical exit_rcu() functions into a single function. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Linus Torvalds Conflicts: kernel/rcupdate.c --- include/linux/rcupdate.h | 1 + include/linux/rcutiny.h | 5 ----- include/linux/rcutree.h | 12 ------------ kernel/rcupdate.c | 28 ++++++++++++++++++++++++++++ kernel/rcutiny_plugin.h | 16 ---------------- kernel/rcutree_plugin.h | 16 ---------------- 6 files changed, 29 insertions(+), 49 deletions(-) (limited to 'include/linux/rcutiny.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index bbfe7854a6a..29665a3b3ac 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -191,6 +191,7 @@ extern void rcu_idle_enter(void); extern void rcu_idle_exit(void); extern void rcu_irq_enter(void); extern void rcu_irq_exit(void); +extern void exit_rcu(void); /** * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 080b5bdda28..adb5e5a38ca 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -87,10 +87,6 @@ static inline void kfree_call_rcu(struct rcu_head *head, #ifdef CONFIG_TINY_RCU -static inline void exit_rcu(void) -{ -} - static inline int rcu_needs_cpu(int cpu) { return 0; @@ -98,7 +94,6 @@ static inline int rcu_needs_cpu(int cpu) #else /* #ifdef CONFIG_TINY_RCU */ -extern void exit_rcu(void); int rcu_preempt_needs_cpu(void); static inline int rcu_needs_cpu(int cpu) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index e8ee5dd0854..782a8ab51bc 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -45,18 +45,6 @@ static inline void rcu_virt_note_context_switch(int cpu) rcu_note_context_switch(cpu); } -#ifdef CONFIG_TREE_PREEMPT_RCU - -extern void exit_rcu(void); - -#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ - -static inline void exit_rcu(void) -{ -} - -#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ - extern void synchronize_rcu_bh(void); extern void synchronize_sched_expedited(void); extern void synchronize_rcu_expedited(void); diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index a86f1741cc2..95cba41ce1e 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -51,6 +51,34 @@ #include "rcu.h" +#ifdef CONFIG_PREEMPT_RCU + +/* + * Check for a task exiting while in a preemptible-RCU read-side + * critical section, clean up if so. No need to issue warnings, + * as debug_check_no_locks_held() already does this if lockdep + * is enabled. + */ +void exit_rcu(void) +{ + struct task_struct *t = current; + + if (likely(list_empty(¤t->rcu_node_entry))) + return; + t->rcu_read_lock_nesting = 1; + barrier(); + t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; + __rcu_read_unlock(); +} + +#else /* #ifdef CONFIG_PREEMPT_RCU */ + +void exit_rcu(void) +{ +} + +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ + #ifdef CONFIG_DEBUG_LOCK_ALLOC static struct lock_class_key rcu_lock_key; struct lockdep_map rcu_lock_map = diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 22ecea0dfb6..fc31a2d6510 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -851,22 +851,6 @@ int rcu_preempt_needs_cpu(void) return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; } -/* - * Check for a task exiting while in a preemptible -RCU read-side - * critical section, clean up if so. No need to issue warnings, - * as debug_check_no_locks_held() already does this if lockdep - * is enabled. - */ -void exit_rcu(void) -{ - struct task_struct *t = current; - - if (t->rcu_read_lock_nesting == 0) - return; - t->rcu_read_lock_nesting = 1; - __rcu_read_unlock(); -} - #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ #ifdef CONFIG_RCU_TRACE diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index b1ac22e6fa3..4936fff820e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -969,22 +969,6 @@ static void __init __rcu_init_preempt(void) rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); } -/* - * Check for a task exiting while in a preemptible-RCU read-side - * critical section, clean up if so. No need to issue warnings, - * as debug_check_no_locks_held() already does this if lockdep - * is enabled. - */ -void exit_rcu(void) -{ - struct task_struct *t = current; - - if (t->rcu_read_lock_nesting == 0) - return; - t->rcu_read_lock_nesting = 1; - __rcu_read_unlock(); -} - #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ static struct rcu_state *rcu_state = &rcu_sched_state; -- cgit v1.2.3-70-g09d2