diff -r c051f521e0be sys/sys/pcpu.h
--- a/sys/sys/pcpu.h	Mon Jun 07 22:43:37 2010 +0000
+++ b/sys/sys/pcpu.h	Thu Jun 10 13:35:01 2010 +1000
@@ -106,6 +106,17 @@
 #define	DPCPU_ID_GET(i, n)	(*DPCPU_ID_PTR(i, n))
 #define	DPCPU_ID_SET(i, n, v)	(*DPCPU_ID_PTR(i, n) = v)
 
+/*
+ * Utility macros.
+ */
+#define DPCPU_SUM(n, var, sum)						\
+do {									\
+	(sum) = 0;							\
+	for (u_int i = mp_maxid; i >= 0; i--)				\
+		if (!CPU_ABSENT(i))					\
+			(sum) += (DPCPU_ID_PTR(i, n))->var;		\
+} while (0)
+
 /* 
  * XXXUPS remove as soon as we have per cpu variable
  * linker sets and can define rm_queue in _rm_lock.h