Add a preemption point when a mutex or condition variable is

handed-off/signaled to a higher priority thread.  Note that when
there are idle KSEs that could run the higher priority thread,
we still add the preemption point because it seems to take the
kernel a while to schedule an idle KSE.  The drawbacks are that
threads will be swapped more often between CPUs (KSEs) and
that there will be an extra userland context switch (the idle
KSE is still woken and will probably resume the preempted
thread).  We'll revisit this if and when idle CPU/KSE wakeup
times improve.

Inspired by:	Petri Helenius <pete@he.iki.fi>
Reviewed by:	davidxu

1 files changed, 10 insertions, 6 deletions

diff --git a/lib/libpthread/thread/thr_mutex.c b/lib/libpthread/thread/thr_mutex.c
index 8d0d76c..c2c28e0 100644
--- a/lib/libpthread/thread/thr_mutex.c
+++ b/lib/libpthread/thread/thr_mutex.c
@@ -859,8 +859,8 @@ mutex_self_lock(struct pthread *curthread, pthread_mutex_t m)
 static int
 mutex_unlock_common(pthread_mutex_t *m, int add_reference)
 {
-	struct pthread	*curthread = _get_curthread();
-	int	ret = 0;
+	struct pthread *curthread = _get_curthread();
+	int ret = 0;
 
 	if (m == NULL || *m == NULL)
 		ret = EINVAL;
@@ -997,7 +997,7 @@ mutex_unlock_common(pthread_mutex_t *m, int add_reference)
 				 */
 				THR_SCHED_LOCK(curthread, curthread);
 				curthread->inherited_priority =
-				    (*m)->m_saved_prio;
+					(*m)->m_saved_prio;
 				curthread->active_priority =
 				    MAX(curthread->inherited_priority,
 				    curthread->base_priority);
@@ -1006,7 +1006,6 @@ mutex_unlock_common(pthread_mutex_t *m, int add_reference)
 				 * This thread now owns one less priority mutex.
 				 */
 				curthread->priority_mutex_count--;
-				THR_SCHED_UNLOCK(curthread, curthread);
 
 				/* Remove the mutex from the threads queue. */
 				MUTEX_ASSERT_IS_OWNED(*m);
@@ -1464,7 +1463,7 @@ _mutex_lock_backout(struct pthread *curthread)
 static void
 mutex_handoff(struct pthread *curthread, struct pthread_mutex *mutex)
 {
-	struct pthread	*pthread;
+	struct pthread *pthread;
 
 	/* Keep dequeueing until we find a valid thread: */
 	mutex->m_owner = NULL;
@@ -1566,8 +1565,13 @@ mutex_handoff(struct pthread *curthread, struct pthread_mutex *mutex)
 
 		/* Make the thread runnable and unlock the scheduling queue: */
 		_thr_setrunnable_unlocked(pthread);
-		THR_SCHED_UNLOCK(curthread, pthread);
 
+		/* Add a preemption point. */
+		if ((curthread->kseg == pthread->kseg) &&
+		    (pthread->active_priority > curthread->active_priority))
+			curthread->critical_yield = 1;
+
+		THR_SCHED_UNLOCK(curthread, pthread);
 		if (mutex->m_owner == pthread)
 			/* We're done; a valid owner was found. */
 			break;