From: Mathieu Desnoyers Date: Mon, 28 Sep 2009 23:44:36 +0000 (-0400) Subject: urcu (signal/mb): use linked list instead of array for registry. X-Git-Tag: v0.1~19 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=e3b0cef0b290dcc757347989a6288c9952efc54a;p=urcu.git urcu (signal/mb): use linked list instead of array for registry. Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-static.h b/urcu-static.h index 0a23ee5..f2a463c 100644 --- a/urcu-static.h +++ b/urcu-static.h @@ -36,6 +36,7 @@ #include #include +#include /* * Identify a shared load. A smp_rmc() or smp_mc() should come before the load. @@ -218,7 +219,14 @@ static inline void reader_barrier() */ extern long urcu_gp_ctr; -extern long __thread urcu_active_readers; +struct urcu_reader { + long ctr; + struct list_head head; + pthread_t tid; + char need_mb; +}; + +extern struct urcu_reader __thread urcu_reader; extern int gp_futex; @@ -253,17 +261,17 @@ static inline void _rcu_read_lock(void) { long tmp; - tmp = urcu_active_readers; + tmp = urcu_reader.ctr; /* 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)); + _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_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.ctr, tmp + RCU_GP_COUNT); } } @@ -271,21 +279,19 @@ static inline void _rcu_read_unlock(void) { long tmp; - tmp = urcu_active_readers; + tmp = urcu_reader.ctr; /* * Finish using rcu before decrementing the pointer. * See force_mb_all_threads(). */ 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 */ + _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT); + /* write urcu_reader.ctr before read futex */ reader_barrier(); wake_up_gp(); } else { - _STORE_SHARED(urcu_active_readers, - urcu_active_readers - RCU_GP_COUNT); + _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT); } } diff --git a/urcu.c b/urcu.c index b323711..d441355 100644 --- a/urcu.c +++ b/urcu.c @@ -63,25 +63,17 @@ long urcu_gp_ctr = RCU_GP_COUNT; * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread urcu_active_readers; +struct urcu_reader __thread urcu_reader; /* Thread IDs of registered readers */ #define INIT_NUM_THREADS 4 -struct reader_registry { - pthread_t tid; - long *urcu_active_readers; - char *need_mb; -}; - #ifdef DEBUG_YIELD unsigned int yield_active; unsigned int __thread rand_yield; #endif -static struct reader_registry *registry; -static char __thread need_mb; -static int num_readers, alloc_readers; +static LIST_HEAD(registry); static void internal_urcu_lock(void) { @@ -100,9 +92,9 @@ static void internal_urcu_lock(void) perror("Error in pthread mutex lock"); exit(-1); } - if (need_mb) { + if (urcu_reader.need_mb) { smp_mb(); - need_mb = 0; + urcu_reader.need_mb = 0; smp_mb(); } poll(NULL,0,10); @@ -130,7 +122,7 @@ static void switch_next_urcu_qparity(void) } #ifdef URCU_MB -static void force_mb_single_thread(struct reader_registry *index) +static void force_mb_single_thread(struct urcu_reader *index) { smp_mb(); } @@ -140,16 +132,16 @@ static void force_mb_all_threads(void) smp_mb(); } #else /* #ifdef URCU_MB */ -static void force_mb_single_thread(struct reader_registry *index) +static void force_mb_single_thread(struct urcu_reader *index) { - assert(registry); + assert(!list_empty(®istry)); /* * pthread_kill has a smp_mb(). But beware, we assume it performs * a cache flush on architectures with non-coherent cache. Let's play * safe and don't assume anything : we use smp_mc() to make sure the * cache flush is enforced. */ - *index->need_mb = 1; + index->need_mb = 1; smp_mc(); /* write ->need_mb before sending the signals */ pthread_kill(index->tid, SIGURCU); smp_mb(); @@ -157,7 +149,7 @@ static void force_mb_single_thread(struct reader_registry *index) * Wait for sighandler (and thus mb()) to execute on every thread. * BUSY-LOOP. */ - while (*index->need_mb) { + while (index->need_mb) { poll(NULL, 0, 1); } smp_mb(); /* read ->need_mb before ending the barrier */ @@ -165,12 +157,13 @@ static void force_mb_single_thread(struct reader_registry *index) static void force_mb_all_threads(void) { - struct reader_registry *index; + struct urcu_reader *index; + /* * Ask for each threads to execute a smp_mb() so we can consider the * compiler barriers around rcu read lock as real memory barriers. */ - if (!registry) + if (list_empty(®istry)) return; /* * pthread_kill has a smp_mb(). But beware, we assume it performs @@ -178,8 +171,8 @@ static void force_mb_all_threads(void) * safe and don't assume anything : we use smp_mc() to make sure the * cache flush is enforced. */ - for (index = registry; index < registry + num_readers; index++) { - *index->need_mb = 1; + list_for_each_entry(index, ®istry, head) { + index->need_mb = 1; smp_mc(); /* write need_mb before sending the signal */ pthread_kill(index->tid, SIGURCU); } @@ -196,8 +189,8 @@ static void force_mb_all_threads(void) * relevant bug report. For Linux kernels, we recommend getting * the Linux Test Project (LTP). */ - for (index = registry; index < registry + num_readers; index++) { - while (*index->need_mb) { + list_for_each_entry(index, ®istry, head) { + while (index->need_mb) { pthread_kill(index->tid, SIGURCU); poll(NULL, 0, 1); } @@ -209,11 +202,11 @@ static void force_mb_all_threads(void) /* * synchronize_rcu() waiting. Single thread. */ -static void wait_gp(struct reader_registry *index) +static void wait_gp(struct urcu_reader *index) { uatomic_dec(&gp_futex); force_mb_single_thread(index); /* Write futex before read reader_gp */ - if (!rcu_old_gp_ongoing(index->urcu_active_readers)) { + if (!rcu_old_gp_ongoing(&index->ctr)) { /* Read reader_gp before write futex */ force_mb_single_thread(index); /* Callbacks are queued, don't wait. */ @@ -229,17 +222,17 @@ static void wait_gp(struct reader_registry *index) void wait_for_quiescent_state(void) { - struct reader_registry *index; + struct urcu_reader *index; - if (!registry) + if (list_empty(®istry)) return; /* - * Wait for each thread urcu_active_readers count to become 0. + * Wait for each thread urcu_reader.ctr count to become 0. */ - for (index = registry; index < registry + num_readers; index++) { + list_for_each_entry(index, ®istry, head) { int wait_loops = 0; #ifndef HAS_INCOHERENT_CACHES - while (rcu_old_gp_ongoing(index->urcu_active_readers)) { + while (rcu_old_gp_ongoing(&index->ctr)) { if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) { wait_gp(index); } else { @@ -249,9 +242,9 @@ void wait_for_quiescent_state(void) #else /* #ifndef HAS_INCOHERENT_CACHES */ /* * BUSY-LOOP. Force the reader thread to commit its - * urcu_active_readers update to memory if we wait for too long. + * urcu_reader.ctr update to memory if we wait for too long. */ - while (rcu_old_gp_ongoing(index->urcu_active_readers)) { + while (rcu_old_gp_ongoing(&index->ctr)) { switch (wait_loops++) { case RCU_QS_ACTIVE_ATTEMPTS: wait_gp(index); @@ -391,67 +384,21 @@ void *rcu_publish_content_sym(void **p, void *v) return oldptr; } -static void rcu_add_reader(pthread_t id) -{ - struct reader_registry *oldarray; - - if (!registry) { - alloc_readers = INIT_NUM_THREADS; - num_readers = 0; - registry = - malloc(sizeof(struct reader_registry) * alloc_readers); - } - if (alloc_readers < num_readers + 1) { - oldarray = registry; - registry = malloc(sizeof(struct reader_registry) - * (alloc_readers << 1)); - memcpy(registry, oldarray, - sizeof(struct reader_registry) * alloc_readers); - alloc_readers <<= 1; - free(oldarray); - } - registry[num_readers].tid = id; - /* reference to the TLS of _this_ reader thread. */ - registry[num_readers].urcu_active_readers = &urcu_active_readers; - registry[num_readers].need_mb = &need_mb; - num_readers++; -} - -/* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. - */ -static void rcu_remove_reader(pthread_t id) -{ - struct reader_registry *index; - - assert(registry != NULL); - for (index = registry; index < registry + num_readers; index++) { - if (pthread_equal(index->tid, id)) { - memcpy(index, ®istry[num_readers - 1], - sizeof(struct reader_registry)); - registry[num_readers - 1].tid = 0; - registry[num_readers - 1].urcu_active_readers = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); -} - void rcu_register_thread(void) { internal_urcu_lock(); urcu_init(); /* In case gcc does not support constructor attribute */ - rcu_add_reader(pthread_self()); + urcu_reader.tid = pthread_self(); + assert(urcu_reader.need_mb == 0); + assert(urcu_reader.ctr == 0); + list_add(&urcu_reader.head, ®istry); internal_urcu_unlock(); } void rcu_unregister_thread(void) { internal_urcu_lock(); - rcu_remove_reader(pthread_self()); + list_del(&urcu_reader.head); internal_urcu_unlock(); } @@ -464,7 +411,7 @@ static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context) * executed on. */ smp_mb(); - need_mb = 0; + urcu_reader.need_mb = 0; smp_mb(); } @@ -506,6 +453,6 @@ void urcu_exit(void) exit(-1); } assert(act.sa_sigaction == sigurcu_handler); - free(registry); + assert(list_empty(®istry)); } #endif /* #ifndef URCU_MB */