diff --git a/benchmark/bm_vm_thread_pass_flood.rb b/benchmark/bm_vm_thread_pass_flood.rb
index 27157d1a6f..a660aafc18 100644
--- a/benchmark/bm_vm_thread_pass_flood.rb
+++ b/benchmark/bm_vm_thread_pass_flood.rb
@@ -1,3 +1,5 @@
+# n.b. this is a good test for GVL when pinned to a single CPU
+
 1000.times{
   Thread.new{loop{Thread.pass}}
 }