CPU - (System) Load Average

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1 - About

The performance load metrics in the context of a system. This metrics is often called a CPU Load average but this is really a system load average as Unix refers it as the run-queue length. Ie:

  • the sum of the number of processes that are currently running
  • plus the number that are waiting (queued) to run.

See also: CPU - (Metrics|Counter)

CPU load can be compared with car traffic. “Cars” are processes:

  • using a slice of CPU time (“crossing the bridge”)
  • or queued up to use the CPU.
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3 - Amount meaning

3.1 - Single Processor

For one core:

  • 0.00 means there's no traffic. Between 0.00 and 1.00 means there's no wait an arriving process will just go right on.
  • 1.00 means the CPU is exactly at capacity. All is still good, but if traffic gets a little heavier, things are going to slow down.
  • over 1.00 means there's backup. How much? Well, 2.00 means that there is 2 CPU to process the whole traffic. – 1CPU working, and one CPU waiting..

To not wait, the CPU load should ideally stay below 1.00.

Rule of Thumb: 0.70 If your load average is staying above > 0.70, it's time to investigate before things get worse.

3.2 - Multi-processor

On multi-processor system, the load is relative to the number of processor cores available. A load of 1.00 is 100% CPU utilization on single-core box. On a dual-core box, a load of 2.00 is 100% CPU utilization.

The total number of cores is what matters, regardless of how many physical processors those cores are spread across.

4 - Example on Linux

grep 'model name' /proc/cpuinfo | wc -l
40
# The max load is then 40

CPU On linux (Uptime and top):

# uptime or top output
12:54:11 up 326 days, 10:56,  1 user,  load average: 0.11, 0.08, 0.09

where

  • 0.11 is the average over the last minute,
  • 0.08 is the average over the last five minutes,
  • and 0.09 is the average over the last 15 minutes

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5 - Documentation / Reference

counter/resource/system/cpu/load.txt · Last modified: 2018/12/14 16:43 by gerardnico