From 4f8e33808fdc08d3182a656d509fe42487d19b86 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Mon, 28 Sep 2009 19:55:42 -0400 Subject: [PATCH] urcu-qsbr: use linked list instead of array for registry Signed-off-by: Mathieu Desnoyers --- urcu-qsbr-static.h | 23 ++++++++---- urcu-qsbr.c | 92 ++++++++++------------------------------------ 2 files changed, 34 insertions(+), 81 deletions(-) diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h index 0d73bcf..1cac56c 100644 --- a/urcu-qsbr-static.h +++ b/urcu-qsbr-static.h @@ -38,6 +38,7 @@ #include #include +#include /* * Identify a shared load. A smp_rmc() or smp_mc() should come before the load. @@ -103,7 +104,7 @@ /* * If a reader is really non-cooperative and refuses to commit its - * rcu_reader_qs_gp count to memory (there is no barrier in the reader + * urcu_reader.ctr count to memory (there is no barrier in the reader * per-se), kick it after a few loops waiting for it. */ #define KICK_READER_LOOPS 10000 @@ -182,7 +183,13 @@ static inline void reader_barrier() */ extern unsigned long urcu_gp_ctr; -extern unsigned long __thread rcu_reader_qs_gp; +struct urcu_reader { + unsigned long ctr; + struct list_head head; + pthread_t tid; +}; + +extern struct urcu_reader __thread urcu_reader; extern int gp_futex; @@ -222,7 +229,7 @@ static inline int rcu_gp_ongoing(unsigned long *value) static inline void _rcu_read_lock(void) { - rcu_assert(rcu_reader_qs_gp); + rcu_assert(urcu_reader.ctr); } static inline void _rcu_read_unlock(void) @@ -232,8 +239,8 @@ static inline void _rcu_read_unlock(void) static inline void _rcu_quiescent_state(void) { smp_mb(); - _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr)); - smp_mb(); /* write rcu_reader_qs_gp before read futex */ + _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr)); + smp_mb(); /* write urcu_reader.ctr before read futex */ wake_up_gp(); smp_mb(); } @@ -241,14 +248,14 @@ static inline void _rcu_quiescent_state(void) static inline void _rcu_thread_offline(void) { smp_mb(); - STORE_SHARED(rcu_reader_qs_gp, 0); - smp_mb(); /* write rcu_reader_qs_gp before read futex */ + STORE_SHARED(urcu_reader.ctr, 0); + smp_mb(); /* write urcu_reader.ctr before read futex */ wake_up_gp(); } static inline void _rcu_thread_online(void) { - _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); smp_mb(); } diff --git a/urcu-qsbr.c b/urcu-qsbr.c index f5103ee..c603c1d 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -50,23 +50,14 @@ unsigned long urcu_gp_ctr = RCU_GP_ONLINE; * Written to only by each individual reader. Read by both the reader and the * writers. */ -unsigned long __thread rcu_reader_qs_gp; - -/* Thread IDs of registered readers */ -#define INIT_NUM_THREADS 4 - -struct reader_registry { - pthread_t tid; - unsigned long *rcu_reader_qs_gp; -}; +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 int num_readers, alloc_readers; +static LIST_HEAD(registry); static void internal_urcu_lock(void) { @@ -104,11 +95,11 @@ static void internal_urcu_unlock(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); smp_mb(); /* Write futex before read reader_gp */ - if (!rcu_gp_ongoing(index->rcu_reader_qs_gp)) { + if (!rcu_gp_ongoing(&index->ctr)) { /* Read reader_gp before write futex */ smp_mb(); /* Callbacks are queued, don't wait. */ @@ -124,17 +115,17 @@ static void wait_gp(struct reader_registry *index) static 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 rcu_reader_qs_gp count to become 0. */ - for (index = registry; index < registry + num_readers; index++) { + list_for_each_entry(index, ®istry, head) { int wait_loops = 0; - while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) { + while (rcu_gp_ongoing(&index->ctr)) { if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) { wait_gp(index); } else { @@ -166,7 +157,7 @@ void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader_qs_gp; + was_online = urcu_reader.ctr; /* All threads should read qparity before accessing data structure * where new ptr points to. @@ -180,7 +171,7 @@ void synchronize_rcu(void) * threads registered as readers. */ if (was_online) - STORE_SHARED(rcu_reader_qs_gp, 0); + STORE_SHARED(urcu_reader.ctr, 0); internal_urcu_lock(); @@ -229,7 +220,7 @@ void synchronize_rcu(void) * freed. */ if (was_online) - _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); smp_mb(); } #else /* !(BITS_PER_LONG < 64) */ @@ -237,7 +228,7 @@ void synchronize_rcu(void) { unsigned long was_online; - was_online = rcu_reader_qs_gp; + was_online = urcu_reader.ctr; /* * Mark the writer thread offline to make sure we don't wait for @@ -246,7 +237,7 @@ void synchronize_rcu(void) */ smp_mb(); if (was_online) - STORE_SHARED(rcu_reader_qs_gp, 0); + STORE_SHARED(urcu_reader.ctr, 0); internal_urcu_lock(); STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); @@ -254,7 +245,7 @@ void synchronize_rcu(void) internal_urcu_unlock(); if (was_online) - _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr)); + _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); smp_mb(); } #endif /* !(BITS_PER_LONG < 64) */ @@ -320,58 +311,13 @@ void rcu_thread_online(void) _rcu_thread_online(); } -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].rcu_reader_qs_gp = &rcu_reader_qs_gp; - 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].rcu_reader_qs_gp = NULL; - num_readers--; - return; - } - } - /* Hrm not found, forgot to register ? */ - assert(0); -} - void rcu_register_thread(void) { + 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(); } @@ -384,6 +330,6 @@ void rcu_unregister_thread(void) */ _rcu_thread_offline(); internal_urcu_lock(); - rcu_remove_reader(pthread_self()); + list_del(&urcu_reader.head); internal_urcu_unlock(); } -- 2.34.1