我的PHP脚本如何判断服务器是否正忙？

$load = sys_getloadavg();
if ($load[0] > 5) {
    // 服务器正忙
}

$top = shell_exec("top -bn1 | grep 'Cpu(s)' | sed 's/.*, *\([0-9.]*\)%* id.*/\1/' | awk '{print 100 - $1}'");
if ($top > 50) {
    // 服务器正忙
}

$free = shell_exec("free | awk '/Mem/{printf(\"%.2f\", $3/$2*100)}'");
if ($free > 80) {
    // 服务器正忙
}

$total = disk_total_space("/");
$free = disk_free_space("/");
$used = $total - $free;
$percent = round(($used / $total) * 100);
if ($percent > 80) {
    // 服务器正忙
}