diff --git a/ChangeLog b/ChangeLog
index ca1dab3ab8..bc17856b23 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Apr 30 16:13:17 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* benchmark/bm_io_select.rb, benchmark/bm_io_select2.rb: New.
+	  based on a patch from Eric Wong at [Feature #4531]
+
 Sat Apr 30 03:25:53 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* test/io/wait/test_io_wait.rb: New. for testing ext/io/wait.
diff --git a/benchmark/bm_io_select.rb b/benchmark/bm_io_select.rb
new file mode 100644
index 0000000000..19248daeb1
--- /dev/null
+++ b/benchmark/bm_io_select.rb
@@ -0,0 +1,9 @@
+# IO.select performance
+
+w = [ IO.pipe[1] ];
+
+nr = 1000000
+nr.times {
+  IO.select nil, w
+}
+
diff --git a/benchmark/bm_io_select2.rb b/benchmark/bm_io_select2.rb
new file mode 100644
index 0000000000..b48651349e
--- /dev/null
+++ b/benchmark/bm_io_select2.rb
@@ -0,0 +1,18 @@
+# IO.select performance. worst case
+
+ios = []
+nr = 1000000
+max = Process.getrlimit(Process::RLIMIT_NOFILE)[0]
+puts "max fd: #{max} (results not apparent with <= 1024 max fd)"
+
+((max / 2) - 2).times do
+  ios.concat IO.pipe
+end
+
+last = [ ios[-1] ]
+puts "last IO: #{last[0].inspect}"
+
+nr.times do
+  IO.select nil, last
+end
+