bench.rb

require 'benchmark_driver'

Benchmark.driver do |x|
  x.prelude %{
    def script
      i = 0
      while i < 1000_000
        i += 1
      end
      i
    end
  }
  x.report 'while', %{ script }
  x.loop_count 2000

  x.verbose
  x.rbenv(
    '2.0.0::2.0.0-p0',
    '2.5.0',
    '2.6.0-preview1',
    '2.6.0-preview1+JIT::2.6.0-preview1,--jit',
    'trunk::after',
    'trunk+JIT::after,--jit',
  )
end

result.txt

2.0.0: ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-linux]
2.5.0: ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]
2.6.0-preview1: ruby 2.6.0preview1 (2018-02-24 trunk 62554) [x86_64-linux]
2.6.0-preview1+JIT: ruby 2.6.0preview1 (2018-02-24 trunk 62554) +JIT [x86_64-linux]
trunk: ruby 2.6.0dev (2018-03-06 trunk 62678) [x86_64-linux]
trunk+JIT: ruby 2.6.0dev (2018-03-06 trunk 62678) +JIT [x86_64-linux]
Calculating -------------------------------------
                          2.0.0       2.5.0  2.6.0-preview1  2.6.0-preview1+JIT       trunk   trunk+JIT
               while     78.377      80.890          86.794             246.379      86.156     493.848 i/s -      2.000k times in 25.517747s 24.724790s 23.043058s 8.117574s 23.213697s 4.049833s

Comparison:
                            while
           trunk+JIT:       493.8 i/s
  2.6.0-preview1+JIT:       246.4 i/s - 2.00x  slower
      2.6.0-preview1:        86.8 i/s - 5.69x  slower
               trunk:        86.2 i/s - 5.73x  slower
               2.5.0:        80.9 i/s - 6.11x  slower
               2.0.0:        78.4 i/s - 6.30x  slower

Use onliner i += 1 while i < 1000_000

How about some other more complicated codes testing? - Rails?

I just tried this script and got pretty much the same speed for ruby 2.0.0, 2.3.0 and 2.5.0.
I was expecting a bit of a difference between 2.0.0 and 2.5.0. Am I doing something wrong here?

2.0.0: ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-darwin17.4.0]
2.3.0: ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin16]
2.5.0: ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin17]
Calculating -------------------------------------
                          2.0.0       2.3.0       2.5.0
               while     58.754      59.356      59.242 i/s -      2.000k times in 34.040247s 33.695179s 33.759657s

Comparison:
                            while
               2.3.0:        59.4 i/s
               2.5.0:        59.2 i/s - 1.00x  slower
               2.0.0:        58.8 i/s - 1.01x  slower

https://github.com/victormartins/learning_examples/blob/ab7491402032c7c892e29e601f0e184a7f042e36/benchmarking/ruby_versions_benchmark.rb#L35-L37

@victormartins, different OS, linux vs mac, can explain the difference.