X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=b7c42fdb0c35deb37e8c5d76a4593746206df0d9;hp=3d576b57441eac3c318f6af6fea2fab7d362ef7d;hb=16aa9ee87cf4364921c36025359be01390338d87;hpb=02be55611d3b1c7bf4fdfcb3a9c98f621882d417 diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 3d576b5..b7c42fd 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -3,7 +3,7 @@ * * Userspace RCU QSBR library * - * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. * * This library is free software; you can redistribute it and/or @@ -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; @@ -59,20 +59,20 @@ unsigned int yield_active; unsigned int __thread rand_yield; #endif -static LIST_HEAD(registry); +static CDS_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); @@ -100,20 +100,41 @@ static void internal_rcu_unlock(void) static void wait_gp(void) { /* Read reader_gp before read futex */ - smp_rmb(); + cmm_smp_rmb(); if (uatomic_read(&gp_futex) == -1) futex_noasync(&gp_futex, FUTEX_WAIT, -1, NULL, NULL, 0); } -static void wait_for_quiescent_state(void) +static void update_counter_and_wait(void) { - LIST_HEAD(qsreaders); + CDS_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 */ + CAA_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); +#else /* !(BITS_PER_LONG < 64) */ + /* Increment current G.P. */ + CAA_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. + */ + cmm_barrier(); + + /* + * Adding a cmm_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. + */ + cmm_smp_mb(); + /* * Wait for each thread rcu_reader_qs_gp count to become 0. */ @@ -122,18 +143,18 @@ static void wait_for_quiescent_state(void) if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { uatomic_dec(&gp_futex); /* Write futex before read reader_gp */ - smp_mb(); + cmm_smp_mb(); } - list_for_each_entry_safe(index, tmp, ®istry, head) { + cds_list_for_each_entry_safe(index, tmp, ®istry, node) { if (!rcu_gp_ongoing(&index->ctr)) - list_move(&index->head, &qsreaders); + cds_list_move(&index->node, &qsreaders); } - if (list_empty(®istry)) { + if (cds_list_empty(®istry)) { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb(); + cmm_smp_mb(); uatomic_set(&gp_futex, 0); } break; @@ -142,15 +163,15 @@ static void wait_for_quiescent_state(void) wait_gp(); } else { #ifndef HAS_INCOHERENT_CACHES - cpu_relax(); + caa_cpu_relax(); #else /* #ifndef HAS_INCOHERENT_CACHES */ - smp_mb(); + cmm_smp_mb(); #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } } /* put back the reader list in the registry */ - list_splice(&qsreaders, ®istry); + cds_list_splice(&qsreaders, ®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; @@ -177,7 +190,7 @@ void synchronize_rcu(void) * where new ptr points to. */ /* Write new ptr before changing the qparity */ - smp_mb(); + cmm_smp_mb(); /* * Mark the writer thread offline to make sure we don't wait for @@ -185,57 +198,48 @@ void synchronize_rcu(void) * threads registered as readers. */ if (was_online) - STORE_SHARED(rcu_reader.ctr, 0); + CAA_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 (cds_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 */ + cmm_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 cmm_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. */ + cmm_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 * freed. */ if (was_online) - _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr)); - smp_mb(); + _CAA_STORE_SHARED(rcu_reader.ctr, CAA_LOAD_SHARED(rcu_gp_ctr)); + cmm_smp_mb(); } #else /* !(BITS_PER_LONG < 64) */ void synchronize_rcu(void) @@ -249,18 +253,20 @@ void synchronize_rcu(void) * our own quiescent state. This allows using synchronize_rcu() in * threads registered as readers. */ - smp_mb(); + cmm_smp_mb(); if (was_online) - STORE_SHARED(rcu_reader.ctr, 0); + CAA_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 (cds_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)); - smp_mb(); + _CAA_STORE_SHARED(rcu_reader.ctr, CAA_LOAD_SHARED(rcu_gp_ctr)); + cmm_smp_mb(); } #endif /* !(BITS_PER_LONG < 64) */ @@ -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); + cds_list_add(&rcu_reader.node, ®istry); + mutex_unlock(&rcu_gp_lock); _rcu_thread_online(); } @@ -311,12 +317,12 @@ 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); + cds_list_del(&rcu_reader.node); + mutex_unlock(&rcu_gp_lock); } void rcu_exit(void) { - assert(list_empty(®istry)); + assert(cds_list_empty(®istry)); }