Index: cam_sim.h
===================================================================
--- cam_sim.h	(revision 227580)
+++ cam_sim.h	(working copy)
@@ -104,7 +104,8 @@
 	u_int32_t		flags;
 #define	CAM_SIM_REL_TIMEOUT_PENDING	0x01
 #define	CAM_SIM_MPSAFE			0x02
-#define CAM_SIM_ON_DONEQ		0x04
+#define	CAM_SIM_ON_DONEQ		0x04
+#define	CAM_SIM_POLLED			0x08
 	struct callout		callout;
 	struct cam_devq 	*devq;	/* Device Queue to use for this SIM */
 	int			refcount; /* References to the SIM. */
Index: cam_xpt.c
===================================================================
--- cam_xpt.c	(revision 227580)
+++ cam_xpt.c	(working copy)
@@ -2957,6 +2957,9 @@
 
 	mtx_assert(sim->mtx, MA_OWNED);
 
+	/* Don't use ISR for this SIM while polling. */
+	sim->flags |= CAM_SIM_POLLED;
+
 	/*
 	 * Steal an opening so that no other queued requests
 	 * can get it before us while we simulate interrupts.
@@ -2996,6 +2999,9 @@
 	} else {
 		start_ccb->ccb_h.status = CAM_RESRC_UNAVAIL;
 	}
+
+	/* Use CAM ISR for this SIM again. */
+	sim->flags &= ~CAM_SIM_POLLED;
 }
 
 /*
@@ -4224,7 +4230,7 @@
 		TAILQ_INSERT_TAIL(&sim->sim_doneq, &done_ccb->ccb_h,
 		    sim_links.tqe);
 		done_ccb->ccb_h.pinfo.index = CAM_DONEQ_INDEX;
-		if ((sim->flags & CAM_SIM_ON_DONEQ) == 0) {
+		if ((sim->flags & (CAM_SIM_ON_DONEQ | CAM_SIM_POLLED)) == 0) {
 			mtx_lock(&cam_simq_lock);
 			first = TAILQ_EMPTY(&cam_simq);
 			TAILQ_INSERT_TAIL(&cam_simq, sim, links);