X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;ds=sidebyside;f=urcu-qsbr.c;h=2cf73d5d5be30f62771a62152623fb81b5798133;hb=5481ddb381061bda64aebc039900d21cac6a6caf;hp=1ac553faefdf20ba1f775fe3af1fd49fd2e698f2;hpb=6abb4bd53503c325dc94b0c0f60b44b9550b462f;p=urcu.git diff --git a/urcu-qsbr.c b/urcu-qsbr.c index 1ac553f..2cf73d5 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 @@ -100,20 +100,41 @@ static void mutex_unlock(pthread_mutex_t *mutex) 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); 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. + */ + 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) { + 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)) { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb(); + cmm_smp_mb(); uatomic_set(&gp_futex, 0); } break; @@ -144,7 +165,7 @@ static void wait_for_quiescent_state(void) #ifndef HAS_INCOHERENT_CACHES cpu_relax(); #else /* #ifndef HAS_INCOHERENT_CACHES */ - smp_mb(); + cmm_smp_mb(); #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ } } @@ -159,14 +180,6 @@ static void wait_for_quiescent_state(void) */ #if (BITS_PER_LONG < 64) -/* - * called with rcu_gp_lock 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 @@ -189,44 +202,35 @@ void synchronize_rcu(void) 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 */ + 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 */ - + update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ +out: mutex_unlock(&rcu_gp_lock); /* @@ -235,7 +239,7 @@ void synchronize_rcu(void) */ if (was_online) _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr)); - smp_mb(); + 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); mutex_lock(&rcu_gp_lock); - STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); - wait_for_quiescent_state(); + 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)); - smp_mb(); + cmm_smp_mb(); } #endif /* !(BITS_PER_LONG < 64) */ @@ -299,7 +305,7 @@ void rcu_register_thread(void) assert(rcu_reader.ctr == 0); mutex_lock(&rcu_gp_lock); - list_add(&rcu_reader.head, ®istry); + list_add(&rcu_reader.node, ®istry); mutex_unlock(&rcu_gp_lock); _rcu_thread_online(); } @@ -312,7 +318,7 @@ void rcu_unregister_thread(void) */ _rcu_thread_offline(); mutex_lock(&rcu_gp_lock); - list_del(&rcu_reader.head); + list_del(&rcu_reader.node); mutex_unlock(&rcu_gp_lock); }