From 0d0e6c21fbf509aebecd5f1c5cbac43a0dc69f6d Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Sun, 20 Sep 2009 11:39:30 -0400 Subject: [PATCH] urcu-defer: Add fast path for empty queues defer_barrier does not need to call synchronize_rcu() when all queues are empty. Skip the G.P. if this is the case. Signed-off-by: Mathieu Desnoyers --- urcu-defer.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) diff --git a/urcu-defer.c b/urcu-defer.c index cd939c7..412eb30 100644 --- a/urcu-defer.c +++ b/urcu-defer.c @@ -133,9 +133,12 @@ static void rcu_defer_barrier_queue(struct defer_queue *queue, static void _rcu_defer_barrier_thread(void) { - unsigned long head; + unsigned long head, num_items; head = defer_queue.head; + num_items = head - defer_queue.tail; + if (unlikely(!num_items)) + return; synchronize_rcu(); rcu_defer_barrier_queue(&defer_queue, head); } @@ -148,20 +151,44 @@ void rcu_defer_barrier_thread(void) internal_urcu_unlock(&urcu_defer_mutex); } +/* + * rcu_defer_barrier - Execute all queued rcu callbacks. + * + * Execute all RCU callbacks queued before rcu_defer_barrier() execution. + * All callbacks queued on the local thread prior to a rcu_defer_barrier() call + * are guaranteed to be executed. + * Callbacks queued by other threads concurrently with rcu_defer_barrier() + * execution are not guaranteed to be executed in the current batch (could + * be left for the next batch). These callbacks queued by other threads are only + * guaranteed to be executed if there is explicit synchronization between + * the thread adding to the queue and the thread issuing the defer_barrier call. + */ + void rcu_defer_barrier(void) { struct deferer_registry *index; + unsigned long num_items = 0; if (!registry) return; internal_urcu_lock(&urcu_defer_mutex); - for (index = registry; index < registry + num_deferers; index++) + for (index = registry; index < registry + num_deferers; index++) { index->last_head = LOAD_SHARED(index->defer_queue->head); + num_items += index->last_head - index->defer_queue->tail; + } + if (likely(!num_items)) { + /* + * We skip the grace period because there are no queued + * callbacks to execute. + */ + goto end; + } synchronize_rcu(); for (index = registry; index < registry + num_deferers; index++) rcu_defer_barrier_queue(index->defer_queue, index->last_head); +end: internal_urcu_unlock(&urcu_defer_mutex); } -- 2.34.1