add script for timing virtio_random driver..

dtrace/virtio_random.d

@@ -0,0 +1,20 @@
+dtrace:::BEGIN
+{
+        tracebegin = timestamp;
+}
+
+dtrace:::END
+{
+        printf("trace length (ms): %d\n", (timestamp - tracebegin) / 1000 / 1000);
+}
+
+::vtrnd_read:entry
+{
+        self->s = timestamp;
+}
+
+::vtrnd_read:return /self->s/
+{
+        @count["count"] = count();
+        @["ns"] = quantize(timestamp - self->s); self->s = 0;
+}