Use Rack::Runtime middleware so the reported time includes the entire middleware stack

actionpack/lib/action_controller/metal/benchmarking.rb

@@ -53,7 +53,6 @@ def process_action(*args)
           log_message << " [#{complete_request_uri rescue "unknown"}]"
 
           logger.info(log_message)
-          response.headers["X-Runtime"] = "%.0f" % ms
         else
           super
         end

railties/lib/rails/application.rb

@@ -208,6 +208,7 @@ def call(env)
     initializer :initialize_middleware_stack do
       if config.frameworks.include?(:action_controller)
         config.middleware.use(::Rack::Lock, :if => lambda { ActionController::Base.allow_concurrency })
+        config.middleware.use(::Rack::Runtime)
         config.middleware.use(ActionDispatch::ShowExceptions, lambda { ActionController::Base.consider_all_requests_local })
         config.middleware.use(ActionDispatch::Callbacks, lambda { ActionController::Dispatcher.prepare_each_request })
         config.middleware.use(lambda { ActionController::Base.session_store }, lambda { ActionController::Base.session_options })