Use [rblineprof](https://github.com/tmm1/rblineprof) for profiling Rails apps

gistfile1.rb

class RBLineProfiler
  WALL_TIME_LIMIT = 10e3 # ms

  def initialize(app)
    @app = app
  end

  def call(env)
    result = nil
    profile = lineprof(/./) { result = @app.call(env) }

    profile.each do |file, line_samples|
      file_lines = nil

      line_samples.each_with_index do |(wall_time, calls), num|
        if wall_time > WALL_TIME_LIMIT
          if !file_lines
            file_lines = File.readlines(file)
            puts file
          end

          printf "% 8.1fms |  %s", wall_time/1000.0, file_lines[num-1]
        end
      end
    end

    result
  end
end

# Add to config/application.rb

config.middleware.use RBLineProfiler