class_CPULoad.php - CPU Load Class
Copyright 2001-2002, Steve Blinch (BlitzAffe Online, http://code.blitzaffe.com)
Latest version available at: http://code.blitzaffe.com
Contact: steve@blitzaffe.com
DESCRIPTION
This script obtains CPU load percentage information from /proc/stat, allowing
the server to display User, Nice, System, Idle, and CPU load percentages to
users.
USAGE
The most important concept to note when using the CPULoad class is that the
CPU load can only be calculated over a period of time. For example, the
script needs to check the current CPU load, wait for a second or two, then
check the CPU load again to get an accurate reading.
There are two ways to do this:
1. When the script is called, it can pause for one or two seconds to get an
accurate reading. While this works, it tends to be cumbersome on busier
sites, since the page takes one or two seconds longer to load.
2. The script can save the CPU data to a file every time it runs, then
refer back to it the next time it is executed. This requires no delay in
processing. The only drawback is that the CPU load is calculated over the
time period between page loads. For example, if the page hasn't been
visited for an hour, the next visitor will see the CPU load average for
the last hour (rather than the current CPU load).
Generally number 2 is the best method.
The most commonly used functions of the CPULoad class are:
CPULoad::sample_load($interval=1)
This function corresponds to method number 1 above. The CPULoad class
checks the CPU load, waits for 1 second, then re-checks the CPU load.
It then calculates the CPU load over that 1 second period.
If you pass a value for $interval, this specifies the number of seconds
to wait between checks. Higher values make for more accurate readings,
but will delay your script's execution.
CPULoad::get_load($fastest_sample=4)
This function corresponds to method number 2 above. The CPULoad class
saves a small file in /tmp/ every time it is called, and uses it to
remember the CPU load information. It then calculates the average
CPU load since the last time it was called.
If you pass a value for $fastest_interval, this specifies the minimum
number of seconds (between page loads) that must elapse before the CPU
load is recalculated. Generally, 4 is good for accurate values.
CPULoad::print_load()
This function outputs the calculated CPU load information.
If you want access to the raw CPU load percentage information, the following
variables are available:
CPULoad->load["user"] - contains the User Mode load percentage
CPULoad->load["nice"] - contains the Low Priority User Mode load percentage
CPULoad->load["system"] - contains the System Mode load percentage
CPULoad->load["idle"] - contains the Idle load percentage
CPULoad->load["cpu"] - contains overall CPU load
CPULoad->cached - contains the number of seconds remaining until the CPU
load is recalculated (if using CPULoad::get_load()).
If these descriptions sound confusing, just try out the sample script included;
it's really simple to use.
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