#include <stdlib.h>
#include <pthread.h>
-#include <syscall.h>
-#include <unistd.h>
+#include <sched.h>
#include <compiler.h>
#include <arch.h>
(_________p1); \
})
-#define futex(...) syscall(__NR_futex, __VA_ARGS__)
-#define FUTEX_WAIT 0
-#define FUTEX_WAKE 1
-
/*
* This code section can only be included in LGPL 2.1 compatible source code.
* See below for the function call wrappers which can be used in code meant to
#define KICK_READER_LOOPS 10000
/*
- * Active attempts to check for reader Q.S. before calling futex().
+ * Active attempts to check for reader Q.S. before calling sched_yield().
*/
#define RCU_QS_ACTIVE_ATTEMPTS 100
/* Use the amount of bits equal to half of the architecture long size */
#define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
+#define RCU_GP_ONGOING (RCU_GP_CTR_BIT << 1)
/*
* Global quiescent period counter with low-order bits unused.
*/
extern long urcu_gp_ctr;
-extern long __thread urcu_active_readers;
-
-extern int gp_futex;
+struct urcu_reader_status {
+ long active_readers;
+ long gp_waiting;
+};
-/*
- * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
- */
-static inline void wake_up_gp(void)
-{
- if (unlikely(atomic_read(&gp_futex) == -1)) {
- atomic_set(&gp_futex, 0);
- futex(&gp_futex, FUTEX_WAKE, 1,
- NULL, NULL, 0);
- }
-}
+extern struct urcu_reader_status __thread urcu_reader_status;
static inline int rcu_old_gp_ongoing(long *value)
{
static inline void _rcu_read_lock(void)
{
- long tmp;
+ long tmp, gp_ctr;
- tmp = urcu_active_readers;
+ tmp = urcu_reader_status.active_readers;
/* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
- _STORE_SHARED(urcu_active_readers, _LOAD_SHARED(urcu_gp_ctr));
+ /*
+ * volatile accesses can be reordered and optimized when within
+ * the same statement.
+ */
+ if (unlikely((gp_ctr = _LOAD_SHARED(urcu_gp_ctr))
+ & RCU_GP_ONGOING) &&
+ unlikely(LOAD_SHARED(urcu_reader_status.gp_waiting))) {
+ sched_yield();
+ gp_ctr = _LOAD_SHARED(urcu_gp_ctr);
+ }
+ _STORE_SHARED(urcu_reader_status.active_readers, gp_ctr);
/*
* Set active readers count for outermost nesting level before
* accessing the pointer. See force_mb_all_threads().
*/
reader_barrier();
} else {
- _STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
+ _STORE_SHARED(urcu_reader_status.active_readers,
+ tmp + RCU_GP_COUNT);
}
}
static inline void _rcu_read_unlock(void)
{
- long tmp;
-
- tmp = urcu_active_readers;
/*
* Finish using rcu before decrementing the pointer.
* See force_mb_all_threads().
+ * Formally only needed for outermost nesting level, but leave barrier
+ * in place for nested unlocks to remove a branch from the common case
+ * (no nesting).
*/
- if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
- reader_barrier();
- _STORE_SHARED(urcu_active_readers,
- urcu_active_readers - RCU_GP_COUNT);
- /* write urcu_active_readers before read futex */
- reader_barrier();
- wake_up_gp();
- } else {
- _STORE_SHARED(urcu_active_readers,
- urcu_active_readers - RCU_GP_COUNT);
- }
+ reader_barrier();
+ _STORE_SHARED(urcu_reader_status.active_readers,
+ urcu_reader_status.active_readers - RCU_GP_COUNT);
}
/**