Calculate execution time of php function

$long_str = "this is a test to see how much time md5 function takes to execute over this string";

// start timing from here
$start = microtime(true);

// function to test
$md5 = md5($long_str);

$elapsed = microtime(true) - $start;

echo "That took $elapsed seconds.n";
?>

执行时间, php