How to make Jruby faster?

The recent Jruby 1.1b should be nearly or faster than matz ruby
implementation. However, when I try to run it for a big source file
~2Mb, I found that Jruby still around 40% slower than matz ruby. (matz
ruby time is not consistent and I think sometimes the GC occur and block
the execution.)

Any suggestion how to optimize Jruby to make it faster?

Here is my result:

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>jruby main.rb
7.776

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>ruby main.rb
4.317

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>jruby main.rb
7.078

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>ruby main.rb
10.128

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>ruby main.rb
1.864

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>ruby main.rb
3.13

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>jruby main.rb
8.713000000000001

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>ruby main.rb
1.845

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>ruby -v
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]

C:\Home\swong24\smv_material\project\ConfigDBParse\lib>jruby -v
ruby 1.8.5 (2007-11-01 rev 4842) [x86-jruby1.1b1]


Here is my code for main.rb:
++++++++++++++++++++++++++++++
require ‘file_parser’
include CfgDBParser

t1 = Time.now;
prepare_file(‘eaglelake.def’)
loadfile
clean_up
puts Time.now - t1
++++++++++++++++++++++++++++++

eaglelake.def is the big src file, around 2MB. Actually it is a special
format database file. I just reformat it to make it become ruby code.