X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu-qsbr-static.h;h=9cc5db493ca1362d1781b44507a10e562623df1f;hb=b3c4dd1a5c12b59efdee51be209767a9f406a715;hp=752d4b9aced8630a94fca3bcf1e6338b012d0e36;hpb=7ac06cef7a7d9394332837edc5c0e9595286a5fc;p=urcu.git

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 752d4b9..9cc5db4 100644
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -32,6 +32,8 @@
 #include <stdlib.h>
 #include <pthread.h>
 #include <assert.h>
+#include <limits.h>
+#include <sched.h>
 
 #include <compiler.h>
 #include <arch.h>
@@ -96,11 +98,16 @@
 
 /*
  * 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
+ * rcu_reader qs_gp 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
 
+/*
+ * Active attempts to check for reader Q.S. before calling sched_yield().
+ */
+#define RCU_QS_ACTIVE_ATTEMPTS 100
+
 #ifdef DEBUG_RCU
 #define rcu_assert(args...)	assert(args)
 #else
@@ -160,26 +167,49 @@ static inline void reader_barrier()
 	smp_mb();
 }
 
+#define RCU_GP_ONLINE		(1UL << 0)
+#define RCU_GP_ONGOING		(1UL << 1)
+#define RCU_GP_CTR		(1UL << 2)
+
 /*
  * Global quiescent period counter with low-order bits unused.
  * Using a int rather than a char to eliminate false register dependencies
  * causing stalls on some architectures.
  */
-extern long urcu_gp_ctr;
+extern unsigned long urcu_gp_ctr;
 
-extern long __thread rcu_reader_qs_gp;
+struct urcu_reader_status {
+	unsigned long qs_gp;
+	unsigned long gp_waiting;
+};
 
-static inline int rcu_gp_ongoing(long *value)
+extern struct urcu_reader_status __thread urcu_reader_status;
+
+#if (BITS_PER_LONG < 64)
+static inline int rcu_gp_ongoing(unsigned long *value)
 {
+	unsigned long reader_gp;
+
 	if (value == NULL)
 		return 0;
+	reader_gp = LOAD_SHARED(*value);
+	return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
+}
+#else /* !(BITS_PER_LONG < 64) */
+static inline int rcu_gp_ongoing(unsigned long *value)
+{
+	unsigned long reader_gp;
 
-	return LOAD_SHARED(*value) & 1;
+	if (value == NULL)
+		return 0;
+	reader_gp = LOAD_SHARED(*value);
+	return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
 }
+#endif  /* !(BITS_PER_LONG < 64) */
 
 static inline void _rcu_read_lock(void)
 {
-	rcu_assert(rcu_reader_qs_gp & 1);
+	rcu_assert(urcu_reader_status.qs_gp);
 }
 
 static inline void _rcu_read_unlock(void)
@@ -188,20 +218,36 @@ static inline void _rcu_read_unlock(void)
 
 static inline void _rcu_quiescent_state(void)
 {
-	smp_mb();	
-	rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr) + 1;
+	long gp_ctr;
+
+	smp_mb();
+	/*
+	 * volatile accesses can be reordered by the compiler when put in the
+	 * same expression.
+	 */
+	if (unlikely((gp_ctr = LOAD_SHARED(urcu_gp_ctr)) & RCU_GP_ONGOING) &&
+	    unlikely(urcu_reader_status.gp_waiting)) {
+		_STORE_SHARED(urcu_reader_status.qs_gp, gp_ctr);
+		sched_yield();
+	} else {
+		_STORE_SHARED(urcu_reader_status.qs_gp, gp_ctr);
+	}
 	smp_mb();
 }
 
 static inline void _rcu_thread_offline(void)
 {
 	smp_mb();
-	rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr);
+	STORE_SHARED(urcu_reader_status.qs_gp, 0);
+	if (unlikely(LOAD_SHARED(urcu_gp_ctr) & RCU_GP_ONGOING) &&
+	    unlikely(urcu_reader_status.gp_waiting)) {
+		sched_yield();
+	}
 }
 
 static inline void _rcu_thread_online(void)
 {
-	rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr) + 1;
+	_STORE_SHARED(urcu_reader_status.qs_gp, LOAD_SHARED(urcu_gp_ctr));
 	smp_mb();
 }
 
@@ -226,6 +272,22 @@ static inline void _rcu_thread_online(void)
 		STORE_SHARED(p, v);			\
 	})
 
+/**
+ * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
+ * is as expected by "old". If succeeds, returns the previous pointer to the
+ * data structure, which can be safely freed after waiting for a quiescent state
+ * using synchronize_rcu(). If fails (unexpected value), returns old (which
+ * should not be freed !).
+ */
+
+#define _rcu_cmpxchg_pointer(p, old, _new)		\
+	({						\
+		if (!__builtin_constant_p(_new) ||	\
+		    ((_new) != NULL))			\
+			wmb();				\
+		cmpxchg(p, old, _new);			\
+	})
+
 /**
  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
  * pointer to the data structure, which can be safely freed after waiting for a