benchmark: drop all bm_ prefix for legacy driver.rb

benchmark/*.rb is only benchmarks now. We don't need prefixes.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63928 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

benchmark/vm_thread_pipe.rb

@@ -0,0 +1,17 @@
+# Measure small and plenty pipe read/write.
+# A performance may depend on GVL implementation.
+
+lmax = 100_000
+r, w = IO.pipe
+[Thread.new{
+  lmax.times{
+    w.write('a')
+  }
+  p "w:exit"
+}, Thread.new{
+  lmax.times{
+    r.read(1)
+  }
+  p "r:exit"
+}].each{|t| t.join}
+