Add profiling to your rake tasks.

Gemfile

group :development do
  gem "ruby-prof"
end

Rakefile

if ENV["TIMESTAMPS"]
  module Rake
    class Task
      def execute_with_timestamps(*args)
        start = Time.now
        execute_without_timestamps(*args)
        execution_time_in_seconds = Time.now - start
        puts
        printf("%s took %.1f seconds\n", name, execution_time_in_seconds)
      end

      alias_method :execute_without_timestamps, :execute
      alias_method :execute, :execute_with_timestamps
    end
  end
end

if ENV["PROFILE"]
  require "ruby-prof"
  module Rake
    class Task
      def execute_with_profile(*args)
        RubyProf.start
        execute_without_profile(*args)
        result = RubyProf.stop
        printer = RubyProf::CallStackPrinter.new(result)
        printer.print STDOUT, {}
      end

      alias_method :execute_without_profile, :execute
      alias_method :execute, :execute_with_profile
    end
  end
end

usage.sh

TIMESTAMPS=true rake mytask
PROFILE=true rake mytask > /path/to/profile.html