From mboxrd@z Thu Jan 1 00:00:00 1970 From: mathieu.desnoyers@efficios.com (Mathieu Desnoyers) Date: Tue, 30 May 2017 17:10:20 -0400 Subject: [lttng-dev] [RCU PATCH liburcu 2/2] Use workqueue in rculfhash In-Reply-To: <1496178620-14755-1-git-send-email-mathieu.desnoyers@efficios.com> References: <1496178620-14755-1-git-send-email-mathieu.desnoyers@efficios.com> Message-ID: <1496178620-14755-3-git-send-email-mathieu.desnoyers@efficios.com> Signed-off-by: Mathieu Desnoyers --- include/urcu/rculfhash.h | 15 ++++-- src/rculfhash-internal.h | 2 +- src/rculfhash.c | 124 +++++++++++++++++++++++------------------------ 3 files changed, 74 insertions(+), 67 deletions(-) diff --git a/include/urcu/rculfhash.h b/include/urcu/rculfhash.h index 9934422..0789aa5 100644 --- a/include/urcu/rculfhash.h +++ b/include/urcu/rculfhash.h @@ -176,10 +176,17 @@ struct cds_lfht *cds_lfht_new(unsigned long init_size, * need to be informed of the value passed to cds_lfht_new(). * * Return 0 on success, negative error value on error. - * Threads calling this API need to be registered RCU read-side threads. - * cds_lfht_destroy should *not* be called from a RCU read-side critical - * section. It should *not* be called from a call_rcu thread context - * neither. + + * Prior to liburcu 0.10: + * - Threads calling this API need to be registered RCU read-side + * threads. + * - cds_lfht_destroy should *not* be called from a RCU read-side + * critical section. It should *not* be called from a call_rcu thread + * context neither. + * + * Starting from liburcu 0.10, rculfhash implements its own worker + * thread to handle resize operations, which removes RCU requirements on + * cds_lfht_destroy. */ extern int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr); diff --git a/src/rculfhash-internal.h b/src/rculfhash-internal.h index d7cec95..0f8df97 100644 --- a/src/rculfhash-internal.h +++ b/src/rculfhash-internal.h @@ -82,7 +82,7 @@ struct cds_lfht { */ pthread_mutex_t resize_mutex; /* resize mutex: add/del mutex */ pthread_attr_t *resize_attr; /* Resize threads attributes */ - unsigned int in_progress_resize, in_progress_destroy; + unsigned int in_progress_destroy; unsigned long resize_target; int resize_initiated; diff --git a/src/rculfhash.c b/src/rculfhash.c index d7a1f23..b7b8f95 100644 --- a/src/rculfhash.c +++ b/src/rculfhash.c @@ -64,7 +64,7 @@ * - Split-counters are used to keep track of the number of * nodes within the hash table for automatic resize triggering. * - Resize operation initiated by long chain detection is executed by a - * call_rcu thread, which keeps lock-freedom of add and remove. + * worker thread, which keeps lock-freedom of add and remove. * - Resize operations are protected by a mutex. * - The removal operation is split in two parts: first, a "removed" * flag is set in the next pointer within the node to remove. Then, @@ -276,6 +276,8 @@ #include #include #include +#include "workqueue.h" +#include "urcu-die.h" /* * Split-counters lazily update the global counter each 1024 @@ -335,11 +337,11 @@ struct ht_items_count { } __attribute__((aligned(CAA_CACHE_LINE_SIZE))); /* - * rcu_resize_work: Contains arguments passed to RCU worker thread + * resize_work: Contains arguments passed to worker thread * responsible for performing lazy resize. */ -struct rcu_resize_work { - struct rcu_head head; +struct resize_work { + struct urcu_work work; struct cds_lfht *ht; }; @@ -356,6 +358,8 @@ struct partition_resize_work { unsigned long start, unsigned long len); }; +static struct urcu_workqueue *cds_lfht_workqueue; + /* * Algorithm to reverse bits in a word by lookup table, extended to * 64-bit words. @@ -1224,14 +1228,12 @@ void partition_resize_helper(struct cds_lfht *ht, unsigned long i, if (start == 0 && nr_threads > 0) return; fallback: - ht->flavor->thread_online(); fct(ht, i, start, len); - ht->flavor->thread_offline(); } /* * Holding RCU read lock to protect _cds_lfht_add against memory - * reclaim that could be performed by other call_rcu worker threads (ABA + * reclaim that could be performed by other worker threads (ABA * problem). * * When we reach a certain length, we can split this population phase over @@ -1308,7 +1310,7 @@ void init_table(struct cds_lfht *ht, /* * Holding RCU read lock to protect _cds_lfht_remove against memory - * reclaim that could be performed by other call_rcu worker threads (ABA + * reclaim that could be performed by other worker threads (ABA * problem). * For a single level, we logically remove and garbage collect each node. * @@ -1320,8 +1322,9 @@ void init_table(struct cds_lfht *ht, * * Concurrent removal and add operations are helping us perform garbage * collection of logically removed nodes. We guarantee that all logically - * removed nodes have been garbage-collected (unlinked) before call_rcu is - * invoked to free a hole level of bucket nodes (after a grace period). + * removed nodes have been garbage-collected (unlinked) before work + * enqueue is invoked to free a hole level of bucket nodes (after a + * grace period). * * Logical removal and garbage collection can therefore be done in batch * or on a node-per-node basis, as long as the guarantee above holds. @@ -1772,25 +1775,12 @@ int cds_lfht_delete_bucket(struct cds_lfht *ht) */ int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr) { - int ret, was_online; + int ret; - /* Wait for in-flight resize operations to complete */ + /* Cancel ongoing resize operations. */ _CMM_STORE_SHARED(ht->in_progress_destroy, 1); - cmm_smp_mb(); /* Store destroy before load resize */ - was_online = ht->flavor->read_ongoing(); - if (was_online) - ht->flavor->thread_offline(); - /* Calling with RCU read-side held is an error. */ - if (ht->flavor->read_ongoing()) { - ret = -EINVAL; - if (was_online) - ht->flavor->thread_online(); - goto end; - } - while (uatomic_read(&ht->in_progress_resize)) - poll(NULL, 0, 100); /* wait for 100ms */ - if (was_online) - ht->flavor->thread_online(); + /* Wait for in-flight resize operations to complete */ + urcu_workqueue_flush_queued_work(cds_lfht_workqueue); ret = cds_lfht_delete_bucket(ht); if (ret) return ret; @@ -1801,7 +1791,6 @@ int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr) if (ret) ret = -EBUSY; poison_free(ht); -end: return ret; } @@ -1897,7 +1886,6 @@ void _do_cds_lfht_resize(struct cds_lfht *ht) * Resize table, re-do if the target size has changed under us. */ do { - assert(uatomic_read(&ht->in_progress_resize)); if (CMM_LOAD_SHARED(ht->in_progress_destroy)) break; ht->resize_initiated = 1; @@ -1930,71 +1918,47 @@ void resize_target_update_count(struct cds_lfht *ht, void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size) { - int was_online; - - was_online = ht->flavor->read_ongoing(); - if (was_online) - ht->flavor->thread_offline(); - /* Calling with RCU read-side held is an error. */ - if (ht->flavor->read_ongoing()) { - static int print_once; - - if (!CMM_LOAD_SHARED(print_once)) - fprintf(stderr, "[error] rculfhash: cds_lfht_resize " - "called with RCU read-side lock held.\n"); - CMM_STORE_SHARED(print_once, 1); - assert(0); - goto end; - } resize_target_update_count(ht, new_size); CMM_STORE_SHARED(ht->resize_initiated, 1); pthread_mutex_lock(&ht->resize_mutex); _do_cds_lfht_resize(ht); pthread_mutex_unlock(&ht->resize_mutex); -end: - if (was_online) - ht->flavor->thread_online(); } static -void do_resize_cb(struct rcu_head *head) +void do_resize_cb(struct urcu_work *work) { - struct rcu_resize_work *work = - caa_container_of(head, struct rcu_resize_work, head); - struct cds_lfht *ht = work->ht; + struct resize_work *resize_work = + caa_container_of(work, struct resize_work, work); + struct cds_lfht *ht = resize_work->ht; - ht->flavor->thread_offline(); + ht->flavor->register_thread(); pthread_mutex_lock(&ht->resize_mutex); _do_cds_lfht_resize(ht); pthread_mutex_unlock(&ht->resize_mutex); - ht->flavor->thread_online(); + ht->flavor->unregister_thread(); poison_free(work); - cmm_smp_mb(); /* finish resize before decrement */ - uatomic_dec(&ht->in_progress_resize); } static void __cds_lfht_resize_lazy_launch(struct cds_lfht *ht) { - struct rcu_resize_work *work; + struct resize_work *work; /* Store resize_target before read resize_initiated */ cmm_smp_mb(); if (!CMM_LOAD_SHARED(ht->resize_initiated)) { - uatomic_inc(&ht->in_progress_resize); - cmm_smp_mb(); /* increment resize count before load destroy */ if (CMM_LOAD_SHARED(ht->in_progress_destroy)) { - uatomic_dec(&ht->in_progress_resize); return; } work = malloc(sizeof(*work)); if (work == NULL) { dbg_printf("error allocating resize work, bailing out\n"); - uatomic_dec(&ht->in_progress_resize); return; } work->ht = ht; - ht->flavor->update_call_rcu(&work->head, do_resize_cb); + urcu_workqueue_queue_work(cds_lfht_workqueue, + &work->work, do_resize_cb); CMM_STORE_SHARED(ht->resize_initiated, 1); } } @@ -2045,3 +2009,39 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size, } __cds_lfht_resize_lazy_launch(ht); } + +static void cds_lfht_fork_prepare(void) +{ + urcu_workqueue_pause_worker(cds_lfht_workqueue); +} + +static void cds_lfht_fork_parent(void) +{ + urcu_workqueue_resume_worker(cds_lfht_workqueue); +} + +static void cds_lfht_fork_child(void) +{ + urcu_workqueue_create_worker(cds_lfht_workqueue); +} + +static void __attribute__((constructor)) cds_lfht_init_worker(void) +{ + int ret; + + if (cds_lfht_workqueue) + return; + cds_lfht_workqueue = urcu_workqueue_create(0, -1, NULL, + NULL, NULL, NULL, NULL, NULL, NULL, NULL); + ret = pthread_atfork(cds_lfht_fork_prepare, + cds_lfht_fork_parent, cds_lfht_fork_child); + if (ret) { + urcu_die(ret); + } +} + +static void __attribute__((destructor)) cds_lfht_fini_worker(void) +{ + urcu_workqueue_destroy(cds_lfht_workqueue); + cds_lfht_workqueue = NULL; +} -- 2.1.4