Load (computing)
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The system load is a UNIX computing term that describes the amount of work that a computer system is doing. The load average is the system load over a period of time. It is conventionally given as three numbers that represent the system load during the last one, five, and fifteen minute periods.
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Calculating Load Average
An idle computer has a load number of 0. Each process that is using CPU, waiting for CPU or in uninterruptible sleep (usually waiting for disk activity) adds 1 to the load number. The load average is calculated as the exponentially damped moving average of the load number.
Understanding Load Averages for CPU Bound Systems
For single CPU systems that are CPU bound (where there are on average no processes in uninterruptible sleep), you can think of load average as a percentage of system utilization during the past one, five, and fifteen minutes of system operation. For multi-CPU systems divide this percentage by the number of CPU's.
For example, a load average of "3.73 7.98 0.50" on a single CPU system can be interpreted as "the CPU was overloaded by 273% during the last minute, but it was only busy half of the time for the last fifteen minutes".
Rather, this means that this CPU could have handled all of the work scheduled for the last minute if it were 3.73 times as fast (or if there were 2.73 times as many more CPU's), but over the last fifteen minutes it was twice as fast as it needed to be to keep up.
Non Unix and Non Unix-Like Systems
- On Microsoft Windows PC systems, the system load is given an instantaneous percentage of CPU utilization.
Important things to note
Note that the load average is not a measure solely of CPU utilization, it is also a measure of disk I/O and, sometimes, network performance. It is only one factor in overall system performance (and is often the least significant).
Other meanings
Load (program linking and loading)
When loading compiled programs into computer memory, they are linked to the relevant program resources, and then the fully resolved codes were loaded into computer memory, for execution. This type of program is often called a linking loader.
Load (database loading)
When loading data into a database management system, a program designed to read input data, and then place it into database tables, is called a loader.
See also
- uptime for load average
- top for an overall system view
- iostat for IO statistics
- netstat for network statistics
- mpstat for CPU statistics