X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=0e1252fdbba707e4515cbbabe8c8a837a6408c79;hp=3d576b57441eac3c318f6af6fea2fab7d362ef7d;hb=0ecb3fde04135d76545ce55d80abea9aef465b54;hpb=02be55611d3b1c7bf4fdfcb3a9c98f621882d417 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 3d576b5..0e1252f 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -39,7 +39,7 @@ void __attribute__((destructor)) rcu_exit(void); -static pthread_mutex_t rcu_mutex = PTHREAD_MUTEX_INITIALIZER; +static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; int gp_futex; @@ -61,18 +61,18 @@ unsigned int __thread rand_yield; static LIST_HEAD(registry); -static void internal_rcu_lock(void) +static void mutex_lock(pthread_mutex_t *mutex) { int ret; #ifndef DISTRUST_SIGNALS_EXTREME - ret = pthread_mutex_lock(&rcu_mutex); + ret = pthread_mutex_lock(mutex); if (ret) { perror("Error in pthread mutex lock"); exit(-1); } #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ - while ((ret = pthread_mutex_trylock(&rcu_mutex)) != 0) { + while ((ret = pthread_mutex_trylock(mutex)) != 0) { if (ret != EBUSY && ret != EINTR) { printf("ret = %d, errno = %d\n", ret, errno); perror("Error in pthread mutex lock"); @@ -83,11 +83,11 @@ static void internal_rcu_lock(void) #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ } -static void internal_rcu_unlock(void) +static void mutex_unlock(pthread_mutex_t *mutex) { int ret; - ret = pthread_mutex_unlock(&rcu_mutex); + ret = pthread_mutex_unlock(mutex); if (ret) { perror("Error in pthread mutex unlock"); exit(-1); @@ -106,14 +106,35 @@ static void wait_gp(void) NULL, NULL, 0); } -static void wait_for_quiescent_state(void) +static void update_counter_and_wait(void) { LIST_HEAD(qsreaders); int wait_loops = 0; struct rcu_reader *index, *tmp; - if (list_empty(®istry)) - return; +#if (BITS_PER_LONG < 64) + /* Switch parity: 0 -> 1, 1 -> 0 */ + STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); +#else /* !(BITS_PER_LONG < 64) */ + /* Increment current G.P. */ + STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); +#endif /* !(BITS_PER_LONG < 64) */ + + /* + * Must commit rcu_gp_ctr update to memory before waiting for quiescent + * state. Failure to do so could result in the writer waiting forever + * while new readers are always accessing data (no progress). Enforce + * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr. + */ + barrier(); + + /* + * Adding a smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. + */ + smp_mb(); + /* * Wait for each thread rcu_reader_qs_gp count to become 0. */ @@ -125,9 +146,9 @@ static void wait_for_quiescent_state(void) smp_mb(); } - list_for_each_entry_safe(index, tmp, ®istry, head) { + list_for_each_entry_safe(index, tmp, ®istry, node) { if (!rcu_gp_ongoing(&index->ctr)) - list_move(&index->head, &qsreaders); + list_move(&index->node, &qsreaders); } if (list_empty(®istry)) { @@ -159,14 +180,6 @@ static void wait_for_quiescent_state(void) */ #if (BITS_PER_LONG < 64) -/* - * called with rcu_mutex held. - */ -static void switch_next_rcu_qparity(void) -{ - STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); -} - void synchronize_rcu(void) { unsigned long was_online; @@ -187,47 +200,38 @@ void synchronize_rcu(void) if (was_online) STORE_SHARED(rcu_reader.ctr, 0); - internal_rcu_lock(); + mutex_lock(&rcu_gp_lock); - switch_next_rcu_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. - */ + if (list_empty(®istry)) + goto out; /* * Wait for previous parity to be empty of readers. */ - wait_for_quiescent_state(); /* Wait readers in parity 0 */ + update_counter_and_wait(); /* 0 -> 1, 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. + * committing next rcu_gp_ctr update to memory. Failure to do so could + * result in the writer waiting forever while new readers are always + * accessing data (no progress). Enforce compiler-order of load + * rcu_reader ctr before store to rcu_gp_ctr. */ - - switch_next_rcu_qparity(); /* 1 -> 0 */ + barrier(); /* - * 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. + * Adding a smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. */ + smp_mb(); /* * Wait for previous parity to be empty of readers. */ - wait_for_quiescent_state(); /* Wait readers in parity 1 */ - - internal_rcu_unlock(); + update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ +out: + mutex_unlock(&rcu_gp_lock); /* * Finish waiting for reader threads before letting the old ptr being @@ -253,10 +257,12 @@ void synchronize_rcu(void) if (was_online) STORE_SHARED(rcu_reader.ctr, 0); - internal_rcu_lock(); - STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); - wait_for_quiescent_state(); - internal_rcu_unlock(); + mutex_lock(&rcu_gp_lock); + if (list_empty(®istry)) + goto out; + update_counter_and_wait(); +out: + mutex_unlock(&rcu_gp_lock); if (was_online) _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr)); @@ -298,9 +304,9 @@ void rcu_register_thread(void) rcu_reader.tid = pthread_self(); assert(rcu_reader.ctr == 0); - internal_rcu_lock(); - list_add(&rcu_reader.head, ®istry); - internal_rcu_unlock(); + mutex_lock(&rcu_gp_lock); + list_add(&rcu_reader.node, ®istry); + mutex_unlock(&rcu_gp_lock); _rcu_thread_online(); } @@ -311,9 +317,9 @@ void rcu_unregister_thread(void) * with a waiting writer. */ _rcu_thread_offline(); - internal_rcu_lock(); - list_del(&rcu_reader.head); - internal_rcu_unlock(); + mutex_lock(&rcu_gp_lock); + list_del(&rcu_reader.node); + mutex_unlock(&rcu_gp_lock); } void rcu_exit(void)