Code to test relative performace penalty of invalidating the MRI Ruby method cache, versus performing method resolution manually via method_missing. (Edit 1: pinpoint the overhead of Class.new by comparing it to a trivial Object#extend; thanks @joshjordanwhat! Edit 2: added optional warm-up to make JRuby benchmarks make more sense.)

method-cache-test.rb

require 'benchmark'

module A; end

class DefinedMethodStyle
  def bust_cache_class(*);  Class.new;            nil end
  def bust_cache_extend(*); Object.new.extend(A); nil end
  def dont_bust_cache(*);   Object.new;           nil end
end

class MethodMissingStyle
  def _bust_cache_class(*);  Class.new;            nil end
  def _bust_cache_extend(*); Object.new.extend(A); nil end
  def _dont_bust_cache(*);   Object.new;           nil end

  def method_missing(method, *args)
    case method
    when :bust_cache_class  then _bust_cache_class(*args)
    when :bust_cache_extend then _bust_cache_extend(*args)
    when :dont_bust_cache   then _dont_bust_cache(*args)
    end
  end
end

dms = DefinedMethodStyle.new
mms = MethodMissingStyle.new
n = 1_000_000

if ENV['WARM_UP'] # this helps with JRuby benchmarking
  puts "Warming up.\n"
  for i in 1..n
    dms.bust_cache_extend(i); dms.bust_cache_class(i); dms.dont_bust_cache(i)
    mms.bust_cache_extend(i); mms.bust_cache_class(i); mms.dont_bust_cache(i)
  end
end

Benchmark.bm do |bm|
  puts "\n defined methods, not busting cache:"
  bm.report { for i in 1..n; dms.dont_bust_cache(i)   end }

  puts "\n method_missing dispatch, not busting cache:"
  bm.report { for i in 1..n; mms.dont_bust_cache(i)   end }

  puts "\n defined methods, busting cache with trivial Object#extend:"
  bm.report { for i in 1..n; dms.bust_cache_extend(i) end }

  puts "\n defined methods, busting cache with Class.new:"
  bm.report { for i in 1..n; dms.bust_cache_class(i)  end }

  puts "\n method_missing dispatch, busting cache with trivial Object#extend:"
  bm.report { for i in 1..n; mms.bust_cache_extend(i) end }

  puts "\n method_missing dispatch, busting cache with Class.new:"
  bm.report { for i in 1..n; mms.bust_cache_class(i)  end }
end