How to use Rack::RubyProf on ruby 1.9 and rails 3

config.ru

# Workaround for stack level too deep error. see also : http://stackoverflow.com/questions/11692559/ruby-profiler-stack-level-too-deep-error
RubyVM::InstructionSequence.compile_option = {
  :tailcall_optimization => true,
  :trace_instruction => false
}

use Rack::RubyProf, :path => '/tmp/profile'
# specify printers (by default all printers are used)
# use Rack::RubyProf, :path => '/tmp/profile', :printers => {::RubyProf::FlatPrinter => 'flat.txt'}

require ::File.expand_path('../config/environment',  __FILE__)
run XXX::Application

Gemfile

…
gem 'ruby-prof'