X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=bb98a199d5138664c4f2e03b14ca7a45cde93c98;hp=878a550b9291d21a464f5e4c1db9e58f1d741ea3;hb=efafc824ca148c6b2ca7f95dc86d2aaa38d4a923;hpb=332c334642672c5cf5e437f5ab2457ce6cddc21a diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 878a550..bb98a19 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -1,7 +1,7 @@ /* - * urcu.c + * urcu-qsbr.c * - * Userspace RCU library + * Userspace RCU QSBR library * * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. @@ -32,42 +32,36 @@ #include #include -#include "urcu-qsbr.h" +#define BUILD_QSBR_LIB +#include "urcu-qsbr-static.h" /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ -//#include "urcu.h" +#include "urcu-qsbr.h" + +void __attribute__((destructor)) rcu_exit(void); + +static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; -pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; +int gp_futex; /* * Global grace period counter. */ -long urcu_gp_ctr = 0; +unsigned long urcu_gp_ctr = RCU_GP_ONLINE; /* * Written to only by each individual reader. Read by both the reader and the * writers. */ -long __thread rcu_reader_qs_gp; - -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 - -struct reader_registry { - pthread_t tid; - long *rcu_reader_qs_gp; - char *need_mb; -}; +struct urcu_reader __thread urcu_reader; #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); -void internal_urcu_lock(void) +static void internal_urcu_lock(void) { int ret; @@ -84,17 +78,12 @@ void internal_urcu_lock(void) perror("Error in pthread mutex lock"); exit(-1); } - if (need_mb) { - smp_mb(); - need_mb = 0; - smp_mb(); - } poll(NULL,0,10); } #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -void internal_urcu_unlock(void) +static void internal_urcu_unlock(void) { int ret; @@ -105,60 +94,175 @@ void internal_urcu_unlock(void) } } -#ifdef HAS_INCOHERENT_CACHES -static void force_mb_single_thread(struct reader_registry *index) -{ - smp_mb(); -} -#endif /* #ifdef HAS_INCOHERENT_CACHES */ - -static void force_mb_all_threads(void) +/* + * synchronize_rcu() waiting. Single thread. + */ +static void wait_gp(void) { - smp_mb(); + /* Read reader_gp before read futex */ + smp_rmb(); + if (uatomic_read(&gp_futex) == -1) + futex(&gp_futex, FUTEX_WAIT, -1, + NULL, NULL, 0); } -void wait_for_quiescent_state(void) +static void wait_for_quiescent_state(void) { - struct reader_registry *index; + LIST_HEAD(qsreaders); + int wait_loops = 0; + struct urcu_reader *index, *tmp; - if (!registry) + if (list_empty(®istry)) return; /* * Wait for each thread rcu_reader_qs_gp count to become 0. */ - for (index = registry; index < registry + num_readers; index++) { -#ifndef HAS_INCOHERENT_CACHES - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) - cpu_relax(); -#else /* #ifndef HAS_INCOHERENT_CACHES */ - int wait_loops = 0; - /* - * BUSY-LOOP. Force the reader thread to commit its - * rcu_reader_qs_gp update to memory if we wait for too long. - */ - while (rcu_gp_ongoing(index->rcu_reader_qs_gp) && - (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) { - if (wait_loops++ == KICK_READER_LOOPS) { - force_mb_single_thread(index); - wait_loops = 0; + for (;;) { + wait_loops++; + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + uatomic_dec(&gp_futex); + /* Write futex before read reader_gp */ + smp_mb(); + } + + list_for_each_entry_safe(index, tmp, ®istry, head) { + if (!rcu_gp_ongoing(&index->ctr)) + list_move(&index->head, &qsreaders); + } + + if (list_empty(®istry)) { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + /* Read reader_gp before write futex */ + smp_mb(); + uatomic_set(&gp_futex, 0); + } + break; + } else { + if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { + wait_gp(); } else { +#ifndef HAS_INCOHERENT_CACHES cpu_relax(); +#else /* #ifndef HAS_INCOHERENT_CACHES */ + smp_mb(); +#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } -#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } + /* put back the reader list in the registry */ + list_splice(&qsreaders, ®istry); +} + +/* + * Using a two-subphases algorithm for architectures with smaller than 64-bit + * long-size to ensure we do not encounter an overflow bug. + */ + +#if (BITS_PER_LONG < 64) +/* + * called with urcu_mutex held. + */ +static void switch_next_urcu_qparity(void) +{ + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR); } void synchronize_rcu(void) { + unsigned long was_online; + + was_online = urcu_reader.ctr; + + /* All threads should read qparity before accessing data structure + * where new ptr points to. + */ + /* Write new ptr before changing the qparity */ + smp_mb(); + + /* + * Mark the writer thread offline to make sure we don't wait for + * our own quiescent state. This allows using synchronize_rcu() in + * threads registered as readers. + */ + if (was_online) + STORE_SHARED(urcu_reader.ctr, 0); + internal_urcu_lock(); - force_mb_all_threads(); - urcu_gp_ctr += 2; + + switch_next_urcu_qparity(); /* 0 -> 1 */ + + /* + * Must commit qparity update to memory before waiting for parity + * 0 quiescent state. Failure to do so could result in the writer + * waiting forever while new readers are always accessing data (no + * progress). + * Ensured by STORE_SHARED and LOAD_SHARED. + */ + + /* + * Wait for previous parity to be empty of readers. + */ + wait_for_quiescent_state(); /* Wait readers in parity 0 */ + + /* + * Must finish waiting for quiescent state for parity 0 before + * committing qparity update to memory. Failure to do so could result in + * the writer waiting forever while new readers are always accessing + * data (no progress). + * Ensured by STORE_SHARED and LOAD_SHARED. + */ + + switch_next_urcu_qparity(); /* 1 -> 0 */ + + /* + * Must commit qparity update to memory before waiting for parity + * 1 quiescent state. Failure to do so could result in the writer + * waiting forever while new readers are always accessing data (no + * progress). + * Ensured by STORE_SHARED and LOAD_SHARED. + */ + + /* + * Wait for previous parity to be empty of readers. + */ + wait_for_quiescent_state(); /* Wait readers in parity 1 */ + + internal_urcu_unlock(); + + /* + * Finish waiting for reader threads before letting the old ptr being + * freed. + */ + if (was_online) + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); + smp_mb(); +} +#else /* !(BITS_PER_LONG < 64) */ +void synchronize_rcu(void) +{ + unsigned long was_online; + + was_online = urcu_reader.ctr; + + /* + * Mark the writer thread offline to make sure we don't wait for + * our own quiescent state. This allows using synchronize_rcu() in + * threads registered as readers. + */ + smp_mb(); + if (was_online) + STORE_SHARED(urcu_reader.ctr, 0); + + internal_urcu_lock(); + STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); wait_for_quiescent_state(); - force_mb_all_threads(); internal_urcu_unlock(); + + if (was_online) + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); + smp_mb(); } +#endif /* !(BITS_PER_LONG < 64) */ /* * library wrappers to be used by non-LGPL compatible source code. @@ -182,13 +286,19 @@ void *rcu_dereference(void *p) void *rcu_assign_pointer_sym(void **p, void *v) { wmb(); - return STORE_SHARED(p, v); + return STORE_SHARED(*p, v); +} + +void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new) +{ + wmb(); + return uatomic_cmpxchg(p, old, _new); } void *rcu_xchg_pointer_sym(void **p, void *v) { wmb(); - return xchg(p, v); + return uatomic_xchg(p, v); } void *rcu_publish_content_sym(void **p, void *v) @@ -200,61 +310,30 @@ void *rcu_publish_content_sym(void **p, void *v) return oldptr; } -static void rcu_add_reader(pthread_t id) +void rcu_quiescent_state(void) { - struct reader_registry *oldarray; + _rcu_quiescent_state(); +} - 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].rcu_reader_qs_gp = &rcu_reader_qs_gp; - registry[num_readers].need_mb = &need_mb; - num_readers++; +void rcu_thread_offline(void) +{ + _rcu_thread_offline(); } -/* - * Never shrink (implementation limitation). - * This is O(nb threads). Eventually use a hash table. - */ -static void rcu_remove_reader(pthread_t id) +void rcu_thread_online(void) { - 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].rcu_reader_qs_gp = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); + _rcu_thread_online(); } void rcu_register_thread(void) { - _rcu_thread_online(); + urcu_reader.tid = pthread_self(); + assert(urcu_reader.ctr == 0); + internal_urcu_lock(); - rcu_add_reader(pthread_self()); + list_add(&urcu_reader.head, ®istry); internal_urcu_unlock(); + _rcu_thread_online(); } void rcu_unregister_thread(void) @@ -265,6 +344,11 @@ void rcu_unregister_thread(void) */ _rcu_thread_offline(); internal_urcu_lock(); - rcu_remove_reader(pthread_self()); + list_del(&urcu_reader.head); internal_urcu_unlock(); } + +void rcu_exit(void) +{ + assert(list_empty(®istry)); +}