diff --git a/ChangeLog b/ChangeLog
index 25c48002c4..31f7af99c5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jun 30 02:41:47 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* thread.c (rb_thread_schedule_limits): minor optimization.
+	  eliminate machine context saving when running time is enough small.
+
 Thu Jun 30 02:28:11 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread.c (rb_thread_schedule_rec): move interrupt_flag check to
diff --git a/thread.c b/thread.c
index 31b9d4fb68..0e10768129 100644
--- a/thread.c
+++ b/thread.c
@@ -1008,15 +1008,13 @@ rb_thread_schedule_limits(unsigned long limits_us)
     if (!rb_thread_alone()) {
 	rb_thread_t *th = GET_THREAD();
 
-	thread_debug("rb_thread_schedule/switch start\n");
-
-	RB_GC_SAVE_MACHINE_CONTEXT(th);
-
-	if (th->running_time_us >= limits_us)
+	if (th->running_time_us >= limits_us) {
+	    thread_debug("rb_thread_schedule/switch start\n");
+	    RB_GC_SAVE_MACHINE_CONTEXT(th);
 	    gvl_yield(th->vm, th);
-
-	rb_thread_set_current(th);
-	thread_debug("rb_thread_schedule/switch done\n");
+	    rb_thread_set_current(th);
+	    thread_debug("rb_thread_schedule/switch done\n");
+	}
     }
 }