Can I throttle the max CPU usage of a php script?

Question

I have some scripts that use a ton of cpu is it possible to cap the amount of cpu a process is allowed to use? I am running on CentOs 5.5 by the way.

Answer 1

PHP is considered a scripting language, and does not have such low level access to the hardware.

Instead, what you can do is use functions like "set_time_limit()"

http://php.net/manual/en/function.set-time-limit.php

and memory_limit in your php.ini

http://php.net/manual/en/ini.core.php

Those are the recommended methods, but the closest you'll get to what you want are probably a combination of "sleep()"

http://php.net/manual/en/function.sleep.php

and getting the current CPU load with "exec('uptime');". Note that you may or may not have access to those system commands.

Answer 2

maybe you could use nice?

Answer 3

I helped a fellow PHP coder create PHP scripts which address a similar issue. These are long-running PHP scripts which generate a lot of load. Since they're long running, the goal was to "pause" them if load gets too high. The script has a function similar to:

function get_server_load()
{
    $fh = fopen('/proc/loadavg', 'r')
    $data = fread($fh, 6);
    fclose($fh);
    $load_avg = explode(" ", $data);
    return floatval(trim($load_avg[0]));
}

The script calls get_server_load() during each loop, and if the load is greater than a given max, it sleeps for 30 seconds and checks again:

set_time_limit(120);
while(get_server_load() > $max_load)
    sleep($load_sleep_time);

This allows the script to give CPU time back to the server during periods of high load.