Index: sys/dev/iommu/iommu_gas.c
===================================================================
--- sys/dev/iommu/iommu_gas.c
+++ sys/dev/iommu/iommu_gas.c
@@ -35,6 +35,7 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/counter.h>
 #include <sys/malloc.h>
 #include <sys/bus.h>
 #include <sys/interrupt.h>
@@ -372,12 +373,19 @@
 	a->entry->flags = IOMMU_MAP_ENTRY_MAP;
 }
 
+static COUNTER_U64_DEFINE_EARLY(gas_lookup);
+SYSCTL_COUNTER_U64(_hw_iommu, OID_AUTO, gas_lookup, CTLFLAG_RD,
+    &gas_lookup,
+    "Number of gas node accesses");
+
 static int
 iommu_gas_lowermatch(struct iommu_gas_match_args *a, struct iommu_map_entry *entry)
 {
 	struct iommu_map_entry *child;
 
 	child = RB_RIGHT(entry, rb_entry);
+	if (child != NULL && entry->end < a->common->lowaddr)
+		counter_u64_add(gas_lookup, 1);
 	if (child != NULL && entry->end < a->common->lowaddr &&
 	    iommu_gas_match_one(a, entry->end, child->first,
 	    a->common->lowaddr)) {
@@ -389,6 +397,8 @@
 	if (entry->first >= a->common->lowaddr)
 		return (ENOMEM);
 	child = RB_LEFT(entry, rb_entry);
+	if (child != NULL)
+		counter_u64_add(gas_lookup, 1);
 	if (child != NULL && 0 == iommu_gas_lowermatch(a, child))
 		return (0);
 	if (child != NULL && child->last < a->common->lowaddr &&
@@ -398,6 +408,8 @@
 		return (0);
 	}
 	child = RB_RIGHT(entry, rb_entry);
+	if (child != NULL && entry->end >= a->common->lowaddr)
+		counter_u64_add(gas_lookup, 1);
 	if (child != NULL && 0 == iommu_gas_lowermatch(a, child))
 		return (0);
 	return (ENOMEM);
@@ -413,6 +425,8 @@
 	if (entry->last < a->common->highaddr)
 		return (ENOMEM);
 	child = RB_LEFT(entry, rb_entry);
+	if (child != NULL)
+		counter_u64_add(gas_lookup, 1);
 	if (child != NULL && 0 == iommu_gas_uppermatch(a, child))
 		return (0);
 	if (child != NULL && child->last >= a->common->highaddr &&
@@ -422,6 +436,8 @@
 		return (0);
 	}
 	child = RB_RIGHT(entry, rb_entry);
+	if (child != NULL)
+		counter_u64_add(gas_lookup, 1);
 	if (child != NULL && entry->end >= a->common->highaddr &&
 	    iommu_gas_match_one(a, entry->end, child->first,
 	    a->domain->end)) {
@@ -453,6 +469,8 @@
 	a.entry = entry;
 
 	/* Handle lower region. */
+	if (common->lowaddr > 0 ||common->highaddr < domain->end)
+		counter_u64_add(gas_lookup, 1);
 	if (common->lowaddr > 0) {
 		error = iommu_gas_lowermatch(&a,
 		    RB_ROOT(&domain->rb_root));