Promise performance: Pure ruby vs extension

I hacked up methodmissing's promise to rename it to ExtPromise.  Then I edited the benchmark program like so:

require "benchmark"
require "ext/promise/promise"
require "promise"

TESTS = 1000
Benchmark.bmbm do |results|
  # Picked inspect instead of undefined, as the pure-ruby promise will raise an 
  # exception on undefined instead of return the promise value
  results.report("Promise") { TESTS.times { Promise.new{ 1 }.inspect } } #.undefined } }
  results.report("ExtPromise") { TESTS.times { ExtPromise.new{ 1 }.inspect } } #.undefined } }    
  results.report("Promise#==") { TESTS.times { Promise.new{ 1 } == 1 } }
  results.report("ExtPromise#==") { TESTS.times { ExtPromise.new{ 1 } == 1 } }
  results.report("Promise#object_id") { TESTS.times { Promise.new{ 1 }.object_id } }
  results.report("ExtPromise#object_id") { TESTS.times { ExtPromise.new{ 1 }.object_id } }
  results.report("Promise#__send__") { TESTS.times { Promise.new{ 1 }.__send__ :object_id } }
  results.report("ExtPromise#__send__") { TESTS.times { ExtPromise.new{ 1 }.__send__ :object_id } }    
  results.report("Promise (blocking)") { TESTS.times { Promise.new{ IO.read(__FILE__) }.inspect } } #.undefined } }
  results.report("ExtPromise (blocking)") { TESTS.times { ExtPromise.new{ IO.read(__FILE__) }.inspect } } #.undefined } }    
  results.report("Promise#== (blocking)") { TESTS.times { Promise.new{ IO.read(__FILE__) } == 1 } }
  results.report("ExtPromise#== (blocking)") { TESTS.times { ExtPromise.new{ IO.read(__FILE__) } == 1 } }
  results.report("Promise#object_id (blocking)") { TESTS.times { Promise.new{ IO.read(__FILE__) }.object_id } }
  results.report("ExtPromise#object_id (blocking)") { TESTS.times { ExtPromise.new{ IO.read(__FILE__) }.object_id } }
  results.report("Promise#__send__ (blocking)") { TESTS.times { Promise.new{ IO.read(__FILE__) }.__send__ :object_id } }
  results.report("ExtPromise#__send__ (blocking)") { TESTS.times { ExtPromise.new{ IO.read(__FILE__) }.__send__ :object_id } }    
end


The results:

ben:ext-promise ben$ rake bench
(in /Users/ben/Repos/ext-promise)
/opt/local/bin/ruby bench/promise.rb
Rehearsal -------------------------------------------------------------------
Promise                           0.010000   0.000000   0.010000 (  0.008493)
ExtPromise                        0.000000   0.000000   0.000000 (  0.009953)
Promise#==                        0.010000   0.000000   0.010000 (  0.007722)
ExtPromise#==                     0.010000   0.010000   0.020000 (  0.011172)
Promise#object_id                 0.010000   0.000000   0.010000 (  0.008627)
ExtPromise#object_id              0.010000   0.000000   0.010000 (  0.011326)
Promise#__send__                  0.010000   0.000000   0.010000 (  0.008789)
ExtPromise#__send__               0.030000   0.000000   0.030000 (  0.042061)
Promise (blocking)                0.120000   0.020000   0.140000 (  0.136777)
ExtPromise (blocking)             0.040000   0.060000   0.100000 (  0.102843)
Promise#== (blocking)             0.030000   0.020000   0.050000 (  0.048383)
ExtPromise#== (blocking)          0.060000   0.050000   0.110000 (  0.119921)
Promise#object_id (blocking)      0.030000   0.030000   0.060000 (  0.046365)
ExtPromise#object_id (blocking)   0.060000   0.050000   0.110000 (  0.119973)
Promise#__send__ (blocking)       0.020000   0.020000   0.040000 (  0.049523)
ExtPromise#__send__ (blocking)    0.050000   0.050000   0.100000 (  0.106921)
---------------------------------------------------------- total: 0.810000sec

                                      user     system      total        real
Promise                           0.010000   0.000000   0.010000 (  0.008081)
ExtPromise                        0.010000   0.000000   0.010000 (  0.010787)
Promise#==                        0.010000   0.000000   0.010000 (  0.007979)
ExtPromise#==                     0.010000   0.000000   0.010000 (  0.012617)
Promise#object_id                 0.010000   0.000000   0.010000 (  0.007502)
ExtPromise#object_id              0.010000   0.000000   0.010000 (  0.009332)
Promise#__send__                  0.010000   0.000000   0.010000 (  0.007801)
ExtPromise#__send__               0.010000   0.000000   0.010000 (  0.010346)
Promise (blocking)                0.110000   0.020000   0.130000 (  0.134745)
ExtPromise (blocking)             0.050000   0.050000   0.100000 (  0.103976)
Promise#== (blocking)             0.020000   0.020000   0.040000 (  0.046742)
ExtPromise#== (blocking)          0.040000   0.060000   0.100000 (  0.102794)
Promise#object_id (blocking)      0.030000   0.020000   0.050000 (  0.045789)
ExtPromise#object_id (blocking)   0.050000   0.050000   0.100000 (  0.103494)
Promise#__send__ (blocking)       0.020000   0.030000   0.050000 (  0.046701)
ExtPromise#__send__ (blocking)    0.050000   0.050000   0.100000 (  0.106211)