application_controller.rb

  # In development mode, optionally perform a RubyProf profile of any request.
  # Simply pass perform_profile=true in your params.
  def perform_profile
    return yield unless params[:perform_profile]
    require 'ruby-prof'
    RubyProf.start
    yield
    result = RubyProf.stop
    printer = RubyProf::FlatPrinter.new(result)
    File.open("#{Rails.root}/tmp/profile.txt", 'w+') do |f|
      printer.print(f)
    end
  end