diff --git a/include/ucore/timers.h b/include/ucore/timers.h
index 8a94131..7182962 100644
--- a/include/ucore/timers.h
+++ b/include/ucore/timers.h
@@ -113,6 +113,7 @@ void uc_timer_remove(struct UCTimers *timers, struct UCTimer *timer);
 int uc_timers_first(const struct UCTimers *timers, struct timeval *first);
 
 /** Get the number of timers the engine is tracking.
+ * (This function is O(n) )
  *
  * @param timers timer engine to query
  * @return the number of timers the engine keeps