php performance

how can i measure the speed of the performance of php?

by inserting a timer. example

//first a little function to compute the elapsed time
function microtime_diff($a, $b) {
list($a_dec, $a_sec) = explode(" ", $a);
list($b_dec, $b_sec) = explode(" ", $b);
return $b_sec - $a_sec + $b_dec - $a_dec;
}
//then insert this at the startpoint
$start_time = microtime();
//then your code you wan't to clock
for ($i = 0; $i<=100000; $i++){}
// then the endpoint and print
$duration = microtime_diff($start_time, microtime());
echo ('100 000 incrementations took ' . sprintf("%0.3f", $duration) . ' seconds');