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>
@@ -351,6 +352,11 @@
 	return (false);
 }
 
+static COUNTER_U64_DEFINE_EARLY(gas_total);
+SYSCTL_COUNTER_U64(_hw_iommu, OID_AUTO, gas_total, CTLFLAG_RD,
+    &gas_total,
+    "Sum of gas tree sizes");
+
 static void
 iommu_gas_match_insert(struct iommu_gas_match_args *a)
 {
@@ -366,12 +372,18 @@
 	 */
 	a->entry->end = a->entry->start + a->size;
 
+	counter_u64_add(gas_total, a->domain->entries_cnt);
 	found = iommu_gas_rb_insert(a->domain, a->entry);
 	KASSERT(found, ("found dup %p start %jx size %jx",
 	    a->domain, (uintmax_t)a->entry->start, (uintmax_t)a->size));
 	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)
 {
@@ -386,6 +398,8 @@
 	if (entry->first >= a->common->lowaddr)
 		return (ENOMEM);
 	child = RB_RIGHT(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 && entry->end < a->common->lowaddr &&
@@ -395,6 +409,8 @@
 		return (0);
 	}
 	child = RB_LEFT(entry, rb_entry);
+	if (child != NULL)
+		counter_u64_add(gas_lookup, 1);
 	if (child != NULL && child->last < a->common->lowaddr &&
 	    iommu_gas_match_one(a, child->last, entry->start,
 	    a->common->lowaddr)) {
@@ -420,6 +436,8 @@
 	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 &&
@@ -429,6 +447,8 @@
 		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)) {
@@ -460,6 +480,8 @@
 	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));
@@ -791,6 +813,9 @@
 {
 	int error;
 
+	CTR4(KTR_SPARE5,
+	     "iommu_map: domain %p, entries %u, size %jd, offset %d",
+	     domain, domain->entries_cnt, (uintmax_t)size, offset);
 	error = iommu_gas_map(domain, common, size, offset, eflags, flags,
 	    ma, res);