php 计算程序的执行时间

$stime=microtime(true); //获取程序开始执行的时间
$etime=microtime(true);//获取程序执行结束的时间
$total=$etime-$stime;   //计算差值
$str_total = var_export($total, TRUE);
if(substr_count($str_total,"E")){
$float_total = floatval(substr($str_total,5));
$total = $float_total/100000;
}
$this->assign("total",$total);