What is the CPU Utilization ?

About

This page is about the CPU Utilization metrics and is the most important metrics of all CPU metrics

CPU utilization is defined as being:

• the amount of time spend not in the idle task.
• or the percentage of time the processor spends doing work (as opposed to being idle).

Calculation Example

If:

• you have a single core processor fixed at a frequency of 2.0 GHz
• this process can do 2G operations by second (ie 2 billion cycles)
• this CPU processor does 1 billion cycles worth of work in a second

it is 50% utilized for that second.

The CPU utilization is the sum of the usage across all cores.

Therefore on:

• On a dual-core system, the maximum CPU usage is 200% (100% per core).
• On a quad-core system, the maximum CPU usage is 400% (100% per core).

Note on Core

Current processor technology is much more complex. A single processor package may contain multiple cores with dynamically changing frequencies, hardware multithreading, and shared caches. These technological advances can change the behavior of CPU utilization reporting mechanisms and increase the difficulty of performance analysis.

Performance investigation, testing and analysis

If an application (myapp.exe) typically uses 25% CPU on lab test machines, but is using 99% of the CPU on another system, this could be indicative of a performance bug.

Implication with Energy Consumption

CPU utilization has important implications on other system performance characteristics, namely power consumption.

Documentation / Reference

• http://www.brendangregg.com/blog/2017-05-09/cpu-utilization-is-wrong.html