diff --git a/lib/libthr/thread/thr_init.c b/lib/libthr/thread/thr_init.c
index 981941b1d9d..d35834c409b 100644
--- a/lib/libthr/thread/thr_init.c
+++ b/lib/libthr/thread/thr_init.c
@@ -103,6 +103,8 @@ size_t		_thr_guard_default;
 size_t		_thr_stack_default = THR_STACK_DEFAULT;
 size_t		_thr_stack_initial = THR_STACK_INITIAL;
 int		_thr_page_size;
+int		_thr_spinloops;
+int		_thr_yieldloops;
 int		_gc_count;
 struct umutex	_mutex_static_lock = DEFAULT_UMUTEX;
 struct umutex	_cond_static_lock = DEFAULT_UMUTEX;
@@ -423,6 +425,7 @@ init_private(void)
 {
 	size_t len;
 	int mib[2];
+	char *env;
 
 	_thr_umutex_init(&_mutex_static_lock);
 	_thr_umutex_init(&_cond_static_lock);
@@ -452,7 +455,12 @@ init_private(void)
 		_thr_guard_default = _thr_page_size;
 		_pthread_attr_default.guardsize_attr = _thr_guard_default;
 		_pthread_attr_default.stacksize_attr = _thr_stack_default;
-
+		env = getenv("LIBPTHREAD_SPINLOOPS");
+		if (env)
+			_thr_spinloops = atoi(env);
+		env = getenv("LIBPTHREAD_YIELDLOOPS");
+		if (env)
+			_thr_yieldloops = atoi(env);
 		TAILQ_INIT(&_thr_atfork_list);
 	}
 	init_once = 1;
diff --git a/lib/libthr/thread/thr_mutex.c b/lib/libthr/thread/thr_mutex.c
index b1e6d0c770c..2cc3ce0d075 100644
--- a/lib/libthr/thread/thr_mutex.c
+++ b/lib/libthr/thread/thr_mutex.c
@@ -66,12 +66,6 @@
 #define MUTEX_ASSERT_NOT_OWNED(m)
 #endif
 
-/*
- * For adaptive mutexes, how many times to spin doing trylock2
- * before entering the kernel to block
- */
-#define MUTEX_ADAPTIVE_SPINS	200
-
 /*
  * Prototypes
  */
@@ -279,6 +273,16 @@ _pthread_mutex_destroy(pthread_mutex_t *mutex)
 	return (ret);
 }
 
+
+#define ENQUEUE_MUTEX(curthread, m)  					\
+		m->m_owner = curthread;					\
+		/* Add to the list of owned mutexes: */			\
+		MUTEX_ASSERT_NOT_OWNED(m);				\
+		if ((m->m_lock.m_flags & UMUTEX_PRIO_PROTECT) == 0)	\
+			TAILQ_INSERT_TAIL(&curthread->mutexq, m, m_qe);	\
+		else							\
+			TAILQ_INSERT_TAIL(&curthread->pp_mutexq, m, m_qe)
+
 static int
 mutex_trylock_common(struct pthread *curthread, pthread_mutex_t *mutex)
 {
@@ -290,13 +294,7 @@ mutex_trylock_common(struct pthread *curthread, pthread_mutex_t *mutex)
 	m = *mutex;
 	ret = _thr_umutex_trylock(&m->m_lock, id);
 	if (ret == 0) {
-		m->m_owner = curthread;
-		/* Add to the list of owned mutexes. */
-		MUTEX_ASSERT_NOT_OWNED(m);
-		if ((m->m_lock.m_flags & UMUTEX_PRIO_PROTECT) == 0)
-			TAILQ_INSERT_TAIL(&curthread->mutexq, m, m_qe);
-		else
-			TAILQ_INSERT_TAIL(&curthread->pp_mutexq, m, m_qe);
+		ENQUEUE_MUTEX(curthread, m);
 	} else if (m->m_owner == curthread) {
 		ret = mutex_self_trylock(m);
 	} /* else {} */
@@ -348,39 +346,43 @@ mutex_lock_common(struct pthread *curthread, pthread_mutex_t *mutex,
 	struct	pthread_mutex *m;
 	uint32_t	id;
 	int	ret;
+	int	count;
 
 	id = TID(curthread);
 	m = *mutex;
 	ret = _thr_umutex_trylock2(&m->m_lock, id);
 	if (ret == 0) {
-		m->m_owner = curthread;
-		/* Add to the list of owned mutexes: */
-		MUTEX_ASSERT_NOT_OWNED(m);
-		if ((m->m_lock.m_flags & UMUTEX_PRIO_PROTECT) == 0)
-			TAILQ_INSERT_TAIL(&curthread->mutexq, m, m_qe);
-		else
-			TAILQ_INSERT_TAIL(&curthread->pp_mutexq, m, m_qe);
+		ENQUEUE_MUTEX(curthread, m);
 	} else if (m->m_owner == curthread) {
 		ret = mutex_self_lock(m, abstime);
 	} else {
-		/*
-		 * For adaptive mutexes, spin for a bit in the expectation
-		 * that if the application requests this mutex type then
-		 * the lock is likely to be released quickly and it is
-		 * faster than entering the kernel
-		 */
-		if (m->m_type == PTHREAD_MUTEX_ADAPTIVE_NP) {
-			int count = MUTEX_ADAPTIVE_SPINS;
-
-			while (count--) {
+		if (_thr_spinloops != 0 && _thr_is_smp &&
+		    !(m->m_lock.m_flags & UMUTEX_PRIO_PROTECT)) {
+			count = _thr_spinloops;
+			while (count && m->m_lock.m_owner != UMUTEX_UNOWNED) {
+				count--;
+				CPU_SPINWAIT;
+			}
+			if (count) {
 				ret = _thr_umutex_trylock2(&m->m_lock, id);
-				if (ret == 0)
-					break;
-				cpu_spinwait();
+				if (ret == 0) {
+					ENQUEUE_MUTEX(curthread, m);
+					return (ret);
+				}
+			}
+		}
+
+		if (_thr_yieldloops != 0) {
+			count = _thr_yieldloops;
+			while (count--) {
+				_sched_yield();
+				ret = _thr_umutex_trylock2(&m->m_lock, id);
+				if (ret == 0) {
+					ENQUEUE_MUTEX(curthread, m);
+					return (ret);
+				}
 			}
 		}
-		if (ret == 0)
-			goto done;
 
 		if (abstime == NULL) {
 			ret = __thr_umutex_lock(&m->m_lock);
@@ -399,17 +401,8 @@ mutex_lock_common(struct pthread *curthread, pthread_mutex_t *mutex,
 			if (ret == EINTR)
 				ret = ETIMEDOUT;
 		}
-done:
-		if (ret == 0) {
-			m->m_owner = curthread;
-			/* Add to the list of owned mutexes: */
-			MUTEX_ASSERT_NOT_OWNED(m);
-			if ((m->m_lock.m_flags & UMUTEX_PRIO_PROTECT) == 0)
-				TAILQ_INSERT_TAIL(&curthread->mutexq, m, m_qe);
-			else
-				TAILQ_INSERT_TAIL(&curthread->pp_mutexq, m,
-					m_qe);
-		}
+		if (ret == 0)
+			ENQUEUE_MUTEX(curthread, m);
 	}
 	return (ret);
 }
@@ -529,7 +522,6 @@ mutex_self_trylock(pthread_mutex_t m)
 	switch (m->m_type) {
 	case PTHREAD_MUTEX_ERRORCHECK:
 	case PTHREAD_MUTEX_NORMAL:
-	case PTHREAD_MUTEX_ADAPTIVE_NP:
 		ret = EBUSY; 
 		break;
 
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
index ab64bf7a6c7..313074f20bd 100644
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -583,7 +583,9 @@ extern size_t	_thr_guard_default __hidden;
 extern size_t	_thr_stack_default __hidden;
 extern size_t	_thr_stack_initial __hidden;
 extern int	_thr_page_size __hidden;
-extern int	_thr_adaptive_spin __hidden;
+extern int	_thr_spinloops __hidden;
+extern int	_thr_yieldloops __hidden;
+
 /* Garbage thread count. */
 extern int	_gc_count __hidden;
 
@@ -653,6 +655,7 @@ int	_schedparam_to_rtp(int policy, const struct sched_param *param,
 		struct rtprio *rtp) __hidden;
 void	_thread_bp_create(void);
 void	_thread_bp_death(void);
+int	_sched_yield(void);
 
 /* #include <fcntl.h> */
 #ifdef  _SYS_FCNTL_H_