X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-defer.c;h=ccf35116d2b73e63634730a475d09feeb650ae38;hp=00dd3c60b3bcf1a2ea7895b3612953a0203af6f6;hb=ba59a0c7b244a0939a2298fc76a9002436ef9674;hpb=804b437535f97b519db3e8715807950f5818cf27 diff --git a/urcu-defer.c b/urcu-defer.c index 00dd3c6..ccf3511 100644 --- a/urcu-defer.c +++ b/urcu-defer.c @@ -28,11 +28,18 @@ #include #include #include +#include +#include +#include #include "urcu-defer-static.h" /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ #include "urcu-defer.h" +#define futex(...) syscall(__NR_futex, __VA_ARGS__) +#define FUTEX_WAIT 0 +#define FUTEX_WAKE 1 + void __attribute__((destructor)) urcu_defer_exit(void); extern void synchronize_rcu(void); @@ -43,11 +50,13 @@ extern void synchronize_rcu(void); static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER; static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER; +static int defer_thread_futex; + /* * Written to only by each individual deferer. Read by both the deferer and * the reclamation tread. */ -struct defer_queue __thread defer_queue; +static struct defer_queue __thread defer_queue; /* Thread IDs of registered deferers */ #define INIT_NUM_THREADS 4 @@ -62,7 +71,6 @@ static struct deferer_registry *registry; static int num_deferers, alloc_deferers; static pthread_t tid_defer; -static int exit_defer; static void internal_urcu_lock(pthread_mutex_t *mutex) { @@ -81,6 +89,7 @@ static void internal_urcu_lock(pthread_mutex_t *mutex) perror("Error in pthread mutex lock"); exit(-1); } + pthread_testcancel(); poll(NULL,0,10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ @@ -97,6 +106,51 @@ static void internal_urcu_unlock(pthread_mutex_t *mutex) } } +/* + * Wake-up any waiting defer thread. Called from many concurrent threads. + */ +static void wake_up_defer(void) +{ + if (unlikely(atomic_read(&defer_thread_futex) == -1)) { + atomic_set(&defer_thread_futex, 0); + futex(&defer_thread_futex, FUTEX_WAKE, 1, + NULL, NULL, 0); + } +} + +static unsigned long rcu_defer_num_callbacks(void) +{ + unsigned long num_items = 0, head; + struct deferer_registry *index; + + internal_urcu_lock(&urcu_defer_mutex); + for (index = registry; index < registry + num_deferers; index++) { + head = LOAD_SHARED(index->defer_queue->head); + num_items += head - index->defer_queue->tail; + } + internal_urcu_unlock(&urcu_defer_mutex); + return num_items; +} + +/* + * Defer thread waiting. Single thread. + */ +static void wait_defer(void) +{ + atomic_dec(&defer_thread_futex); + smp_mb(); /* Write futex before read queue */ + if (rcu_defer_num_callbacks()) { + smp_mb(); /* Read queue before write futex */ + /* Callbacks are queued, don't wait. */ + atomic_set(&defer_thread_futex, 0); + } else { + smp_rmb(); /* Read queue before read futex */ + if (atomic_read(&defer_thread_futex) == -1) + futex(&defer_thread_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); + } +} + /* * Must be called after Q.S. is reached. */ @@ -116,19 +170,15 @@ static void rcu_defer_barrier_queue(struct defer_queue *queue, smp_rmb(); /* read head before q[]. */ p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]); if (unlikely(DQ_IS_FCT_BIT(p))) { - //printf("%lu fct bit %p\n", i-1, p); DQ_CLEAR_FCT_BIT(p); queue->last_fct_out = p; p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]); } else if (unlikely(p == DQ_FCT_MARK)) { - //printf("%lu fct mark %p\n", i-1, p); p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]); queue->last_fct_out = p; p = LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]); - }// else - //printf("%lu data %p\n", i-1, p); + } fct = queue->last_fct_out; - //printf("tid %lu %lu last_fct %p data %p\n", pthread_self(), i-1, fct, p); fct(p); } smp_mb(); /* push tail after having used q[] */ @@ -137,9 +187,12 @@ static void rcu_defer_barrier_queue(struct defer_queue *queue, static void _rcu_defer_barrier_thread(void) { - unsigned long head; + unsigned long head, num_items; head = defer_queue.head; + num_items = head - defer_queue.tail; + if (unlikely(!num_items)) + return; synchronize_rcu(); rcu_defer_barrier_queue(&defer_queue, head); } @@ -152,28 +205,122 @@ void rcu_defer_barrier_thread(void) internal_urcu_unlock(&urcu_defer_mutex); } +/* + * rcu_defer_barrier - Execute all queued rcu callbacks. + * + * Execute all RCU callbacks queued before rcu_defer_barrier() execution. + * All callbacks queued on the local thread prior to a rcu_defer_barrier() call + * are guaranteed to be executed. + * Callbacks queued by other threads concurrently with rcu_defer_barrier() + * execution are not guaranteed to be executed in the current batch (could + * be left for the next batch). These callbacks queued by other threads are only + * guaranteed to be executed if there is explicit synchronization between + * the thread adding to the queue and the thread issuing the defer_barrier call. + */ + void rcu_defer_barrier(void) { struct deferer_registry *index; + unsigned long num_items = 0; if (!registry) return; internal_urcu_lock(&urcu_defer_mutex); - for (index = registry; index < registry + num_deferers; index++) + for (index = registry; index < registry + num_deferers; index++) { index->last_head = LOAD_SHARED(index->defer_queue->head); + num_items += index->last_head - index->defer_queue->tail; + } + if (likely(!num_items)) { + /* + * We skip the grace period because there are no queued + * callbacks to execute. + */ + goto end; + } synchronize_rcu(); for (index = registry; index < registry + num_deferers; index++) rcu_defer_barrier_queue(index->defer_queue, index->last_head); +end: internal_urcu_unlock(&urcu_defer_mutex); } +/* + * _rcu_defer_queue - Queue a RCU callback. + */ +void _rcu_defer_queue(void (*fct)(void *p), void *p) +{ + unsigned long head, tail; + + /* + * Head is only modified by ourself. Tail can be modified by reclamation + * thread. + */ + head = defer_queue.head; + tail = LOAD_SHARED(defer_queue.tail); + + /* + * If queue is full, empty it ourself. + * Worse-case: must allow 2 supplementary entries for fct pointer. + */ + if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) { + assert(head - tail <= DEFER_QUEUE_SIZE); + rcu_defer_barrier_thread(); + assert(head - LOAD_SHARED(defer_queue.tail) == 0); + } + + if (unlikely(defer_queue.last_fct_in != fct)) { + defer_queue.last_fct_in = fct; + if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) { + /* + * If the function to encode is not aligned or the + * marker, write DQ_FCT_MARK followed by the function + * pointer. + */ + _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], + DQ_FCT_MARK); + _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], + fct); + } else { + DQ_SET_FCT_BIT(fct); + _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], + fct); + } + } else { + if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) { + /* + * If the data to encode is not aligned or the marker, + * write DQ_FCT_MARK followed by the function pointer. + */ + _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], + DQ_FCT_MARK); + _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], + fct); + } + } + _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p); + smp_wmb(); /* Publish new pointer before head */ + /* Write q[] before head. */ + STORE_SHARED(defer_queue.head, head); + smp_mb(); /* Write queue head before read futex */ + /* + * Wake-up any waiting defer thread. + */ + wake_up_defer(); +} + void *thr_defer(void *args) { for (;;) { - if (LOAD_SHARED(exit_defer)) - break; + pthread_testcancel(); + /* + * "Be green". Don't wake up the CPU if there is no RCU work + * to perform whatsoever. Aims at saving laptop battery life by + * leaving the processor in sleep state when idle. + */ + wait_defer(); + /* Sleeping after wait_defer to let many callbacks enqueue */ poll(NULL,0,100); /* wait for 100ms */ rcu_defer_barrier(); } @@ -254,7 +401,8 @@ static void stop_defer_thread(void) int ret; void *tret; - STORE_SHARED(exit_defer, 1); + pthread_cancel(tid_defer); + wake_up_defer(); ret = pthread_join(tid_defer, &tret); assert(!ret); }