How to get web server average load level in percentages using PHP function sys_getloadavg()?

Question

PHP function sys_getloadavg() returns an array with three values showing average number of processes in the system run-queue over the last 1, 5 and 15 minutes, respectively.

How to convert this production to percentages?

Answer 1

Percentages are relative measurement units. This means that we must know a range or minimum and maximum values of the measured quantity. Function sys_getloadavg() evaluates performance of whole system, not separate CPU load level, or usage of memory, file system or database. It returns float numbers showing how many processes were in run-queue for the last interval of time.

I did some experiment with my MacBook Pro (8 CPU cores) and PHP 7.0 to figure out range of values produced by sys_getloadavg(). I've got average figures between 1.3 and 3.2. When I run video conversion program in parallel, the maximum result jumped up to 18.9. By the way, in all cases I didn't fix substantial losses in web page loading speed. It means that whole system was not overloaded.

Let's take for 100% of system load situation when web page don't load for reasonable time, let say 10 sec. I don't know what values will return sys_getloadavg() in this case, but I think it will be something big.

My solution is very simple. Let's measure system average load level and persistently store results as minimum and maximum values. When system works faster or slower we will update min and max by new values. So, our program will 'learn' the system and becomes more and more precise. The value of the last minute will be compared with stored range and converted to percents like (loadavg - min)/((max - min) / 100):

$performance = sys_getloadavg();
try {
  $rangeFile = 'sys_load_level.txt';
  $range = file($rangeFile, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
  $performance = array_merge($performance, $range);
  $min = min($performance);
  $max = max($performance);
  if ($range[0] > $min || $range[1] < $max)
    file_put_contents($rangeFile, [$min.PHP_EOL, $max.PHP_EOL]);
}
catch (Exception $e) {
  $min = min($performance);
  $max = max($performance);
  file_put_contents($rangeFile, [$min.PHP_EOL, $max.PHP_EOL]);
}
$level = intval(($performance[0] - $min) / (($max - $min) / 100.0));