PHP 计算页面加载时间

<?
function getmicrotime() {
list($usec, $sec) = explode(" ",microtime());
return ((float)$usec + (float)$sec);
}
?>

<?
$time_start = getmicrotime();
$time_end = getmicrotime();
$loadtime = $time_end - $time_start;
echo "PHP: loaded in ".round($loadtime,3);
?>