P-states control the operational state of the CPU when it is doing some useful work. For instance,
even if the CPU/core is in C0 state that does not mean it needs to run at its maximum speed. A
very basic example is when using the laptop in battery mode: the CPU will enter a higher P-state
hence reducing the frequency at which the CPU/core runs at to minimize power consumption.
This document does not go into the details of each C/P-state. The following links provide detailed
references:
https://www.hardwaresecrets.com/everything-you-need-to-know-about-the-cpu-c-states-
power-saving-modes/
https://software.intel.com/en-us/blogs/2008/03/12/c-states-and-p-states-are-very-different
https://web.archive.org/web/20170825081029/https://haypo.github.io/intel-cpus.html
https://github.com/HewlettPackard/LinuxKI/wiki/Power-vs-Performance
https://people.cs.pitt.edu/~kirk/cs3150spring2010/ShiminChen.pptx
Whether to enable or disable C/P-states for greater throughput or lower latency depends a lot
on the use case. For instance, in some ultra-low latency applications it is beneficial to disable
the CPU C-states, because when the CPU is always in C0 state, there is no overhead to resume
working.
Similarly, for certain use cases where you want to predict the amount of work performed by
the CPU in a given amount of time, it is beneficial to set the CPU frequency to always run at a
certain speed (for example 3 GHz) and still allow Turbo Boost.
2.1 Cpupower Tool
Use the cpupower tool to read your supported CPU frequencies, and to set them. To install the
tool run the command zypper in cpupower .
As an example, if you run the command # cpupower frequency-info , you can read some
important information from the output:
hardware limits: 1.20 GHz - 2.20 GHz
This represents the frequency range supported by the CPU.
available frequency steps: 2.20 GHz, 2.10 GHz, 2.00 GHz, 1.90 GHz, 1.80 GHz,
1.70 GHz, 1.60 GHz, 1.50 GHz, 1.40 GHz, 1.30 GHz, 1.20 GHz
This represents the values which the frequency can be set to if manually set.
5 Performance Analysis, Tuning and Tools on SUSE Linux Enterprise Products
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