问如何检测jquery ajax请求的持续时间是否超过5秒

EN

$.ajax({
    url: "/ajax_json_echo/",
    type: "GET",
    dataType: "json",
    timeout: 1000,
    success: function(response) { alert(response); },
    error: function(x, t, m) {
        if(t==="timeout") {
            alert("got timeout");
        } else {
            alert(t);
        }
    }
});​

$.ajaxSetup({
     beforeSend: function(jqXHR, settings){

          /* Generate a timer for the request */
          jqXHR.timer = setTimeout(function(){

               /* Ask the user to confirm */
               if(confirm(settings.url + ' is taking too long. Cancel request?')){
                   jqXHR.abort();
               }
          }, 10000);
     }
});

var timer = setTimeout(function() {
    alert('Too long!');
}, 10000);

$.getJSON(url, function() {
   clearTimeout(timer);
});