New version: https://gist.github.com/k0kubun/48cc6777fa0e82dfcd74bf38f4a48222

loop.rb

require 'erb'
require 'shellwords'

methods = Integer(ARGV[0] || 1)
sleep_seconds = methods * 0.15
loop_count = (250000000.0 / methods).to_i

src = ERB.new(<<-'erb', nil, '%').result(binding)
% methods.times do |i|
def call<%= i %>() nil end
call<%= i %>; call<%= i %>; call<%= i %>; call<%= i %>; call<%= i %>;
% end

if ENV['MJIT_ENABLE'] == 'true'
  $stderr.puts "sleeping <%= sleep_seconds %>"
  sleep <%= sleep_seconds %>
end
$stderr.puts "running"

i = 0
before = Process.clock_gettime(Process::CLOCK_MONOTONIC)
while i < <%= loop_count %>
  <%= methods.times.map { |i| "call#{i}; " }.join('') %>
  i += 1
end
after = Process.clock_gettime(Process::CLOCK_MONOTONIC)
puts((after - before).to_s)
$stderr.puts "finish\n"
erb

puts "\n```\n#{src}```\n\n"

results = []

3.times do
  if ENV['MJIT_ENABLE'] == 'true'
    cmd = [RbConfig.ruby, '--disable-gems', '--jit-verbose=1', '--jit-max-cache=10000', '-e']
  else
    cmd = [RbConfig.ruby, '--disable-gems', '-e']
  end
  puts "+ #{cmd.shelljoin} ..."
  result = IO.popen([*cmd, src], &:read)
  results << result
  puts "\n\nResult: #{result}\n\n"
end

puts "Avg: #{results.map(&:strip).map(&:to_f).inject(&:+) / results.size.to_f}"