From: Mathieu Desnoyers Date: Mon, 19 Nov 2012 23:16:53 +0000 (-0500) Subject: urcu-wait: move queue management code into urcu-wait.h X-Git-Tag: v0.8.0~137 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=bf6822a6b57e21a18a01731277355ab2e4eb23f3;p=urcu.git urcu-wait: move queue management code into urcu-wait.h Note: urcu-wait.h is not yet exposed outside of userspace RCU. Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-qsbr.c b/urcu-qsbr.c index d691389..3c2c65d 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -36,7 +36,6 @@ #include #include "urcu/wfcqueue.h" -#include "urcu/wfstack.h" #include "urcu/map/urcu-qsbr.h" #define BUILD_QSBR_LIB #include "urcu/static/urcu-qsbr.h" @@ -80,19 +79,11 @@ DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); static CDS_LIST_HEAD(registry); -struct gp_waiters_thread { - struct cds_wfs_node node; - struct urcu_wait wait; -}; - /* - * Stack keeping threads awaiting to wait for a grace period. Contains + * Queue keeping threads awaiting to wait for a grace period. Contains * struct gp_waiters_thread objects. */ -static struct cds_wfs_stack gp_waiters = { - .head = CDS_WFS_END, - .lock = PTHREAD_MUTEX_INITIALIZER, -}; +static DEFINE_URCU_WAIT_QUEUE(gp_waiters); static void mutex_lock(pthread_mutex_t *mutex) { @@ -214,9 +205,8 @@ void synchronize_rcu(void) CDS_LIST_HEAD(cur_snap_readers); CDS_LIST_HEAD(qsreaders); unsigned long was_online; - struct gp_waiters_thread gp_waiters_thread; - struct cds_wfs_head *gp_waiters_head; - struct cds_wfs_node *waiters_iter, *waiters_iter_n; + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; was_online = URCU_TLS(rcu_reader).ctr; @@ -234,24 +224,24 @@ void synchronize_rcu(void) cmm_smp_mb(); /* - * Add ourself to gp_waiters stack of threads awaiting to wait + * Add ourself to gp_waiters queue of threads awaiting to wait * for a grace period. Proceed to perform the grace period only - * if we are the first thread added into the stack. + * if we are the first thread added into the queue. */ - cds_wfs_node_init(&gp_waiters_thread.node); - urcu_wait_init(&gp_waiters_thread.wait); - if (cds_wfs_push(&gp_waiters, &gp_waiters_node) != 0) { - /* Not first in stack: will be awakened by another thread. */ - urcu_adaptative_busy_wait(&gp_waiters_thread.wait); + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); goto gp_end; } + /* We won't need to wake ourself up */ + urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); mutex_lock(&rcu_gp_lock); /* - * Pop all waiters into our local stack head. + * Move all waiters into our local queue. */ - gp_waiters_head = __cds_wfs_pop_all(&gp_waiters); + urcu_move_waiters(&waiters, &gp_waiters); if (cds_list_empty(®istry)) goto out; @@ -308,19 +298,7 @@ void synchronize_rcu(void) cds_list_splice(&qsreaders, ®istry); out: mutex_unlock(&rcu_gp_lock); - - /* Wake all waiters in our stack head, excluding ourself. */ - cds_wfs_for_each_blocking_safe(gp_waiters_head, waiters_iter, - waiters_iter_n) { - struct gp_waiters_thread *wt; - - wt = caa_container_of(waiters_iter, - struct gp_waiters_thread, node); - if (wt == &gp_waiters_thread) - continue; - urcu_adaptative_wake_up(&wt->wait); - } - + urcu_wake_all_waiters(&waiters); gp_end: /* * Finish waiting for reader threads before letting the old ptr being @@ -336,9 +314,8 @@ void synchronize_rcu(void) { CDS_LIST_HEAD(qsreaders); unsigned long was_online; - struct gp_waiters_thread gp_waiters_thread; - struct cds_wfs_head *gp_waiters_head; - struct cds_wfs_node *waiters_iter, *waiters_iter_n; + DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); + struct urcu_waiters waiters; was_online = URCU_TLS(rcu_reader).ctr; @@ -353,24 +330,24 @@ void synchronize_rcu(void) cmm_smp_mb(); /* - * Add ourself to gp_waiters stack of threads awaiting to wait + * Add ourself to gp_waiters queue of threads awaiting to wait * for a grace period. Proceed to perform the grace period only - * if we are the first thread added into the stack. + * if we are the first thread added into the queue. */ - cds_wfs_node_init(&gp_waiters_thread.node); - urcu_wait_init(&gp_waiters_thread.wait); - if (cds_wfs_push(&gp_waiters, &gp_waiters_thread.node) != 0) { - /* Not first in stack: will be awakened by another thread. */ - urcu_adaptative_busy_wait(&gp_waiters_thread.wait); + if (urcu_wait_add(&gp_waiters, &wait) != 0) { + /* Not first in queue: will be awakened by another thread. */ + urcu_adaptative_busy_wait(&wait); goto gp_end; } + /* We won't need to wake ourself up */ + urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); mutex_lock(&rcu_gp_lock); /* - * Pop all waiters into our local stack head. + * Move all waiters into our local queue. */ - gp_waiters_head = __cds_wfs_pop_all(&gp_waiters); + urcu_move_waiters(&waiters, &gp_waiters); if (cds_list_empty(®istry)) goto out; @@ -405,19 +382,7 @@ void synchronize_rcu(void) cds_list_splice(&qsreaders, ®istry); out: mutex_unlock(&rcu_gp_lock); - - /* Wake all waiters in our stack head, excluding ourself. */ - cds_wfs_for_each_blocking_safe(gp_waiters_head, waiters_iter, - waiters_iter_n) { - struct gp_waiters_thread *wt; - - wt = caa_container_of(waiters_iter, - struct gp_waiters_thread, node); - if (wt == &gp_waiters_thread) - continue; - urcu_adaptative_wake_up(&wt->wait); - } - + urcu_wake_all_waiters(&waiters); gp_end: if (was_online) rcu_thread_online(); diff --git a/urcu-wait.h b/urcu-wait.h index 13f26cc..ff7d2cc 100644 --- a/urcu-wait.h +++ b/urcu-wait.h @@ -24,6 +24,7 @@ */ #include +#include /* * Number of busy-loop attempts before waiting on futex for grace period @@ -36,72 +37,149 @@ enum urcu_wait_state { URCU_WAIT_WAITING = 0, /* non-zero are used as masks. */ URCU_WAIT_WAKEUP = (1 << 0), - URCU_WAIT_AWAKENED = (1 << 1), + URCU_WAIT_RUNNING = (1 << 1), URCU_WAIT_TEARDOWN = (1 << 2), }; -struct urcu_wait { - int32_t futex; +struct urcu_wait_node { + struct cds_wfs_node node; + int32_t state; /* enum urcu_wait_state */ }; +#define URCU_WAIT_NODE_INIT(name, _state) \ + { .state = _state } + +#define DEFINE_URCU_WAIT_NODE(name, state) \ + struct urcu_wait_node name = URCU_WAIT_NODE_INIT(name, state) + +#define DECLARE_URCU_WAIT_NODE(name) \ + struct urcu_wait_node name + +struct urcu_wait_queue { + struct cds_wfs_stack stack; +}; + +#define URCU_WAIT_QUEUE_HEAD_INIT(name) \ + { .stack.head = CDS_WFS_END, .stack.lock = PTHREAD_MUTEX_INITIALIZER } + +#define DECLARE_URCU_WAIT_QUEUE(name) \ + struct urcu_wait_queue name + +#define DEFINE_URCU_WAIT_QUEUE(name) \ + struct urcu_wait_queue name = URCU_WAIT_QUEUE_HEAD_INIT(name) + +struct urcu_waiters { + struct cds_wfs_head *head; +}; + +/* + * Add ourself atomically to a wait queue. Return 0 if queue was + * previously empty, else return 1. + * A full memory barrier is issued before being added to the wait queue. + */ +static inline +bool urcu_wait_add(struct urcu_wait_queue *queue, + struct urcu_wait_node *node) +{ + return cds_wfs_push(&queue->stack, &node->node); +} + +/* + * Atomically move all waiters from wait queue into our local struct + * urcu_waiters. + */ +static inline +void urcu_move_waiters(struct urcu_waiters *waiters, + struct urcu_wait_queue *queue) +{ + waiters->head = __cds_wfs_pop_all(&queue->stack); +} + +static inline +void urcu_wait_set_state(struct urcu_wait_node *node, + enum urcu_wait_state state) +{ + node->state = state; +} + static inline -void urcu_wait_init(struct urcu_wait *wait) +void urcu_wait_node_init(struct urcu_wait_node *node, + enum urcu_wait_state state) { - wait->futex = URCU_WAIT_WAITING; + urcu_wait_set_state(node, state); + cds_wfs_node_init(&node->node); } /* * Note: urcu_adaptative_wake_up needs "value" to stay allocated - * throughout its execution. In this scheme, the waiter owns the futex + * throughout its execution. In this scheme, the waiter owns the node * memory, and we only allow it to free this memory when it receives the * URCU_WAIT_TEARDOWN flag. */ static inline -void urcu_adaptative_wake_up(struct urcu_wait *wait) +void urcu_adaptative_wake_up(struct urcu_wait_node *wait) { cmm_smp_mb(); - assert(uatomic_read(&wait->futex) == URCU_WAIT_WAITING); - uatomic_set(&wait->futex, URCU_WAIT_WAKEUP); - if (!(uatomic_read(&wait->futex) & URCU_WAIT_AWAKENED)) - futex_noasync(&wait->futex, FUTEX_WAKE, 1, NULL, NULL, 0); + assert(uatomic_read(&wait->state) == URCU_WAIT_WAITING); + uatomic_set(&wait->state, URCU_WAIT_WAKEUP); + if (!(uatomic_read(&wait->state) & URCU_WAIT_RUNNING)) + futex_noasync(&wait->state, FUTEX_WAKE, 1, NULL, NULL, 0); /* Allow teardown of struct urcu_wait memory. */ - uatomic_or(&wait->futex, URCU_WAIT_TEARDOWN); + uatomic_or(&wait->state, URCU_WAIT_TEARDOWN); } /* * Caller must initialize "value" to URCU_WAIT_WAITING before passing its * memory to waker thread. */ -static void urcu_adaptative_busy_wait(struct urcu_wait *wait) +static inline +void urcu_adaptative_busy_wait(struct urcu_wait_node *wait) { unsigned int i; - /* Load and test condition before read futex */ + /* Load and test condition before read state */ cmm_smp_rmb(); for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) { - if (uatomic_read(&wait->futex) != URCU_WAIT_WAITING) + if (uatomic_read(&wait->state) != URCU_WAIT_WAITING) goto skip_futex_wait; caa_cpu_relax(); } - futex_noasync(&wait->futex, FUTEX_WAIT, + futex_noasync(&wait->state, FUTEX_WAIT, URCU_WAIT_WAITING, NULL, NULL, 0); skip_futex_wait: - /* Tell waker thread than we are awakened. */ - uatomic_or(&wait->futex, URCU_WAIT_AWAKENED); + /* Tell waker thread than we are runnning. */ + uatomic_or(&wait->state, URCU_WAIT_RUNNING); /* * Wait until waker thread lets us know it's ok to tear down * memory allocated for struct urcu_wait. */ for (i = 0; i < URCU_WAIT_ATTEMPTS; i++) { - if (uatomic_read(&wait->futex) & URCU_WAIT_TEARDOWN) + if (uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN) break; caa_cpu_relax(); } - while (!(uatomic_read(&wait->futex) & URCU_WAIT_TEARDOWN)) + while (!(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN)) poll(NULL, 0, 10); - assert(uatomic_read(&wait->futex) & URCU_WAIT_TEARDOWN); + assert(uatomic_read(&wait->state) & URCU_WAIT_TEARDOWN); +} + +static inline +void urcu_wake_all_waiters(struct urcu_waiters *waiters) +{ + struct cds_wfs_node *iter, *iter_n; + + /* Wake all waiters in our stack head */ + cds_wfs_for_each_blocking_safe(waiters->head, iter, iter_n) { + struct urcu_wait_node *wait_node = + caa_container_of(iter, struct urcu_wait_node, node); + + /* Don't wake already running threads */ + if (wait_node->state & URCU_WAIT_RUNNING) + continue; + urcu_adaptative_wake_up(wait_node); + } } #endif /* _URCU_WAIT_H */