diff --git a/sys/dev/xen/debug/debug.c b/sys/dev/xen/debug/debug.c
--- a/sys/dev/xen/debug/debug.c
+++ b/sys/dev/xen/debug/debug.c
@@ -58,8 +58,11 @@
 static int
 xendebug_drain(void *arg, const char *str, int len)
 {
-
-	HYPERVISOR_console_write(__DECONST(char *, str), len);
+	/*
+	 * Use xen_emergency_print() instead of xc_printf() to avoid the
+	 * overhead of parsing a format string when it's not needed.
+	 */
+	xen_emergency_print(str, len);
 	return (len);
 }
 
@@ -75,10 +78,9 @@
 	stack_save(&st);
 
 	mtx_lock_spin(&lock);
-	sbuf_clear(buf);
 	xc_printf("Printing stack trace vCPU%u\n", XEN_VCPUID());
 	stack_sbuf_print_ddb(buf, &st);
-	sbuf_finish(buf);
+	sbuf_drain(buf);
 	mtx_unlock_spin(&lock);
 #endif