Benchmark each require in your Ruby code.

gix_require_benchmark.rb

require 'rubygems'
require 'rbtree'

class Req
  attr_accessor :path, :time, :requires, :exception
  def initialize(path)
    @path = path
    @requires = []
    @time = 0
  end
end

module Kernel
  @@require_stack = [ Req.new('<top>') ]

  alias original_require require

  def require(path)
    req = Req.new(path)
    @@require_stack.last.requires.push(req)
    @@require_stack.push req

    result = nil
    t1 = Time.now

    begin
      result = original_require(path)
    rescue LoadError => e
      req.exception = e
    end

    t2 = Time.now
    req.time = (t2 - t1)

    @@require_stack.pop

    unless req.exception
      result
    else
      raise(req.exception)
    end
  end

  def print_require_tree(req, loaded, level = 0)
    indent = '  ' * level
    fmt = " #{loaded[req.path] ? '(%10.5f)' : ' %10.5f '}  #{indent}%s  %s"
    puts fmt % [ req.time, req.path, req.exception ? "(#{req.exception.message})" : '' ]
    loaded[req.path] = true
    req.requires.each do |r|
      print_require_tree(r, loaded, level + 1)
    end
  end

  at_exit do
    print_require_tree(@@require_stack.first, {})
  end
end

require_benchmark.rb

require 'rubygems'

module Kernel
  @@require_times = {}

  alias original_require require

  def require(path)
    t1 = Time.now
    result = original_require(path)
    t2 = Time.now

    @@require_times[path] = (t2 - t1)

    result
  end

  at_exit do
    @@require_times.sort_by { |path,t| t }.each do |path,t|
      puts "  #{t}\t#{path}"
    end
  end
end

Fixed. The only failed require appears to be fastthread which incurs ~0.09 seconds.