X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-defer.c;h=ccf35116d2b73e63634730a475d09feeb650ae38;hp=412eb30477908b2a60acff9dde794d9ecfc793f8;hb=ba59a0c7b244a0939a2298fc76a9002436ef9674;hpb=0d0e6c21fbf509aebecd5f1c5cbac43a0dc69f6d

diff --git a/urcu-defer.c b/urcu-defer.c
index 412eb30..ccf3511 100644
--- a/urcu-defer.c
+++ b/urcu-defer.c
@@ -28,11 +28,18 @@
 #include <string.h>
 #include <errno.h>
 #include <poll.h>
+#include <sys/time.h>
+#include <syscall.h>
+#include <unistd.h>
 
 #include "urcu-defer-static.h"
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu-defer.h"
 
+#define futex(...)	syscall(__NR_futex, __VA_ARGS__)
+#define FUTEX_WAIT		0
+#define FUTEX_WAKE		1
+
 void __attribute__((destructor)) urcu_defer_exit(void);
 
 extern void synchronize_rcu(void);
@@ -43,11 +50,13 @@ extern void synchronize_rcu(void);
 static pthread_mutex_t urcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
 
+static int defer_thread_futex;
+
 /*
  * Written to only by each individual deferer. Read by both the deferer and
  * the reclamation tread.
  */
-struct defer_queue __thread defer_queue;
+static struct defer_queue __thread defer_queue;
 
 /* Thread IDs of registered deferers */
 #define INIT_NUM_THREADS 4
@@ -62,7 +71,6 @@ static struct deferer_registry *registry;
 static int num_deferers, alloc_deferers;
 
 static pthread_t tid_defer;
-static int exit_defer;
 
 static void internal_urcu_lock(pthread_mutex_t *mutex)
 {
@@ -81,6 +89,7 @@ static void internal_urcu_lock(pthread_mutex_t *mutex)
 			perror("Error in pthread mutex lock");
 			exit(-1);
 		}
+		pthread_testcancel();
 		poll(NULL,0,10);
 	}
 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
@@ -97,6 +106,51 @@ static void internal_urcu_unlock(pthread_mutex_t *mutex)
 	}
 }
 
+/*
+ * Wake-up any waiting defer thread. Called from many concurrent threads.
+ */
+static void wake_up_defer(void)
+{
+	if (unlikely(atomic_read(&defer_thread_futex) == -1)) {
+		atomic_set(&defer_thread_futex, 0);
+		futex(&defer_thread_futex, FUTEX_WAKE, 1,
+		      NULL, NULL, 0);
+	}
+}
+
+static unsigned long rcu_defer_num_callbacks(void)
+{
+	unsigned long num_items = 0, head;
+	struct deferer_registry *index;
+
+	internal_urcu_lock(&urcu_defer_mutex);
+	for (index = registry; index < registry + num_deferers; index++) {
+		head = LOAD_SHARED(index->defer_queue->head);
+		num_items += head - index->defer_queue->tail;
+	}
+	internal_urcu_unlock(&urcu_defer_mutex);
+	return num_items;
+}
+
+/*
+ * Defer thread waiting. Single thread.
+ */
+static void wait_defer(void)
+{
+	atomic_dec(&defer_thread_futex);
+	smp_mb();	/* Write futex before read queue */
+	if (rcu_defer_num_callbacks()) {
+		smp_mb();	/* Read queue before write futex */
+		/* Callbacks are queued, don't wait. */
+		atomic_set(&defer_thread_futex, 0);
+	} else {
+		smp_rmb();	/* Read queue before read futex */
+		if (atomic_read(&defer_thread_futex) == -1)
+			futex(&defer_thread_futex, FUTEX_WAIT, -1,
+			      NULL, NULL, 0);
+	}
+}
+
 /*
  * Must be called after Q.S. is reached.
  */
@@ -192,11 +246,81 @@ end:
 	internal_urcu_unlock(&urcu_defer_mutex);
 }
 
+/*
+ * _rcu_defer_queue - Queue a RCU callback.
+ */
+void _rcu_defer_queue(void (*fct)(void *p), void *p)
+{
+	unsigned long head, tail;
+
+	/*
+	 * Head is only modified by ourself. Tail can be modified by reclamation
+	 * thread.
+	 */
+	head = defer_queue.head;
+	tail = LOAD_SHARED(defer_queue.tail);
+
+	/*
+	 * If queue is full, empty it ourself.
+	 * Worse-case: must allow 2 supplementary entries for fct pointer.
+	 */
+	if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
+		assert(head - tail <= DEFER_QUEUE_SIZE);
+		rcu_defer_barrier_thread();
+		assert(head - LOAD_SHARED(defer_queue.tail) == 0);
+	}
+
+	if (unlikely(defer_queue.last_fct_in != fct)) {
+		defer_queue.last_fct_in = fct;
+		if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
+			/*
+			 * If the function to encode is not aligned or the
+			 * marker, write DQ_FCT_MARK followed by the function
+			 * pointer.
+			 */
+			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+				      DQ_FCT_MARK);
+			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+				      fct);
+		} else {
+			DQ_SET_FCT_BIT(fct);
+			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+				      fct);
+		}
+	} else {
+		if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
+			/*
+			 * If the data to encode is not aligned or the marker,
+			 * write DQ_FCT_MARK followed by the function pointer.
+			 */
+			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+				      DQ_FCT_MARK);
+			_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+				      fct);
+		}
+	}
+	_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
+	smp_wmb();	/* Publish new pointer before head */
+			/* Write q[] before head. */
+	STORE_SHARED(defer_queue.head, head);
+	smp_mb();	/* Write queue head before read futex */
+	/*
+	 * Wake-up any waiting defer thread.
+	 */
+	wake_up_defer();
+}
+
 void *thr_defer(void *args)
 {
 	for (;;) {
-		if (LOAD_SHARED(exit_defer))
-			break;
+		pthread_testcancel();
+		/*
+		 * "Be green". Don't wake up the CPU if there is no RCU work
+		 * to perform whatsoever. Aims at saving laptop battery life by
+		 * leaving the processor in sleep state when idle.
+		 */
+		wait_defer();
+		/* Sleeping after wait_defer to let many callbacks enqueue */
 		poll(NULL,0,100);	/* wait for 100ms */
 		rcu_defer_barrier();
 	}
@@ -277,7 +401,8 @@ static void stop_defer_thread(void)
 	int ret;
 	void *tret;
 
-	STORE_SHARED(exit_defer, 1);
+	pthread_cancel(tid_defer);
+	wake_up_defer();
 	ret = pthread_join(tid_defer, &tret);
 	assert(!ret);
 }