diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 30e4c07..b8a3631 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -450,7 +450,8 @@ _tsleep_wakeup(struct thread *td)
 
 	if (td->td_gd != gd) {
 		lwkt_hold(td);
-		lwkt_send_ipiq(td->td_gd, (ipifunc1_t)tsleep_wakeup_remote, td);
+		lwkt_send_ipiq_adaptive(td->td_gd,
+		    (ipifunc1_t)tsleep_wakeup_remote, td);
 		return;
 	}
 #endif
diff --git a/sys/kern/lwkt_ipiq.c b/sys/kern/lwkt_ipiq.c
index 2235f59..3767cd1 100644
--- a/sys/kern/lwkt_ipiq.c
+++ b/sys/kern/lwkt_ipiq.c
@@ -73,6 +73,8 @@ static __int64_t ipiq_fifofull;	/* number of fifo full conditions detected */
 static __int64_t ipiq_avoided;	/* interlock with target avoids cpu ipi */
 static __int64_t ipiq_passive;	/* passive IPI messages */
 static __int64_t ipiq_cscount;	/* number of cpu synchronizations */
+int ipiq_adaptive_threshold;	/* passive IPI when target cpu lwkt runq length
+				 * approx. greater than this */
 static int ipiq_debug;		/* set to 1 for debug */
 #ifdef PANIC_DEBUG
 static int	panic_ipiq_cpu = -1;
@@ -91,6 +93,9 @@ SYSCTL_QUAD(_lwkt, OID_AUTO, ipiq_passive, CTLFLAG_RW, &ipiq_passive, 0,
     "Number of passive IPI messages sent");
 SYSCTL_QUAD(_lwkt, OID_AUTO, ipiq_cscount, CTLFLAG_RW, &ipiq_cscount, 0,
     "Number of cpu synchronizations");
+SYSCTL_INT(_lwkt, OID_AUTO, ipiq_adapative_threshold, CTLFLAG_RW,
+    &ipiq_adaptive_threshold, 0,
+    "Threshold where adaptive IPI's become passive");
 SYSCTL_INT(_lwkt, OID_AUTO, ipiq_debug, CTLFLAG_RW, &ipiq_debug, 0,
     "");
 #ifdef PANIC_DEBUG
diff --git a/sys/kern/lwkt_thread.c b/sys/kern/lwkt_thread.c
index c55ebdd..b888494 100644
--- a/sys/kern/lwkt_thread.c
+++ b/sys/kern/lwkt_thread.c
@@ -36,7 +36,7 @@
  * Each cpu in a system has its own self-contained light weight kernel
  * thread scheduler, which means that generally speaking we only need
  * to use a critical section to avoid problems.  Foreign thread 
- * scheduling is queued via (async) IPIs.
+ * scheduling is done via IPIs.
  */
 
 #include <sys/param.h>
@@ -243,6 +243,7 @@ _lwkt_dequeue(thread_t td)
 	TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
 	if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
 		atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
+	--gd->gd_lwkt_runq_len;
     }
 }
 
@@ -280,6 +281,8 @@ _lwkt_enqueue(thread_t td)
 	 */
 	if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
 	    need_lwkt_resched();
+
+        ++gd->gd_lwkt_runq_len;
     }
 }
 
@@ -491,7 +494,7 @@ lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
 	TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
 	crit_exit_gd(mygd);
     } else {
-	lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
+        lwkt_send_ipiq_adaptive(gd, lwkt_init_thread_remote, td);
     }
 #else
     crit_enter_gd(mygd);
@@ -974,7 +977,7 @@ lwkt_switch_return(thread_t otd)
 			 (TDF_MIGRATING | TDF_RUNNING));
 		otd->td_migrate_gd = NULL;
 		otd->td_flags &= ~TDF_RUNNING;
-		lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
+		lwkt_send_ipiq_adaptive(rgd, lwkt_setcpu_remote, otd);
 	} else {
 		otd->td_flags &= ~TDF_RUNNING;
 	}
@@ -1314,7 +1317,7 @@ _lwkt_schedule(thread_t td)
 	    _lwkt_enqueue(td);
 	    _lwkt_schedule_post(mygd, td, 1);
 	} else {
-	    lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
+	    lwkt_send_ipiq3_adaptive(td->td_gd, lwkt_schedule_remote, td, 0);
 	}
 #else
 	_lwkt_enqueue(td);
@@ -1447,7 +1450,7 @@ lwkt_deschedule(thread_t td)
 	if (td->td_gd == mycpu) {
 	    _lwkt_dequeue(td);
 	} else {
-	    lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
+            lwkt_send_ipiq_adaptive(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
 	}
     }
 #else
diff --git a/sys/sys/globaldata.h b/sys/sys/globaldata.h
index 51424a3..276e658 100644
--- a/sys/sys/globaldata.h
+++ b/sys/sys/globaldata.h
@@ -166,7 +166,8 @@ struct globaldata {
 	struct systimer	*gd_systimer_inprog;	/* in-progress systimer */
 	int		gd_timer_running;
 	u_int		gd_idle_repeat;		/* repeated switches to idle */
-	int		gd_ireserved[7];
+	int		gd_lwkt_runq_len;	/* size of lwkt run queue */
+	int		gd_ireserved[6];
 	const char	*gd_infomsg;		/* debugging */
 	struct lwkt_tokref gd_handoff;		/* hand-off tokref */
 	void		*gd_preserved[8];	/* future fields */
diff --git a/sys/sys/thread2.h b/sys/sys/thread2.h
index 250c4a5..2d3484f 100644
--- a/sys/sys/thread2.h
+++ b/sys/sys/thread2.h
@@ -29,6 +29,8 @@
 #endif
 #include <machine/cpufunc.h>
 
+extern int ipiq_adaptive_threshold;
+
 /*
  * Is a token held by the specified thread?
  */
@@ -311,6 +313,16 @@ lwkt_send_ipiq_passive(globaldata_t target, ipifunc1_t func, void *arg)
 }
 
 static __inline int
+lwkt_send_ipiq_adaptive(globaldata_t target, ipifunc1_t func, void *arg)
+{
+    if (ipiq_adaptive_threshold > 0 &&
+        target->gd_lwkt_runq_len >= ipiq_adaptive_threshold)
+        return(lwkt_send_ipiq3_passive(target, (ipifunc3_t)func, arg, 0));
+    else
+        return(lwkt_send_ipiq3(target, (ipifunc3_t)func, arg, 0));
+}
+
+static __inline int
 lwkt_send_ipiq2_passive(globaldata_t target, ipifunc2_t func, 
 		       void *arg1, int arg2)
 {
@@ -329,6 +341,17 @@ lwkt_send_ipiq2_bycpu(int dcpu, ipifunc2_t func, void *arg1, int arg2)
     return(lwkt_send_ipiq3_bycpu(dcpu, (ipifunc3_t)func, arg1, arg2));
 }
 
+static __inline int
+lwkt_send_ipiq3_adaptive(globaldata_t target, ipifunc3_t func, void *arg,
+    int arg2)
+{
+    if (ipiq_adaptive_threshold > 0 &&
+        target->gd_lwkt_runq_len >= ipiq_adaptive_threshold)
+        return(lwkt_send_ipiq3_passive(target, func, arg, arg2));
+    else
+        return(lwkt_send_ipiq3(target, func, arg, arg2));
+}
+
 #endif	/* SMP */
 #endif	/* _KERNEL */
 #endif	/* _SYS_THREAD2_H_ */