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In this video, I'll tell you about process priority and cgroups.

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Because earlier you have learned about the NICE command.

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Now how does that relate to cgroups?

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Well, easy.

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If no cgroups resource allocation has been used, all processes are equal.

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And that's shown by the priority parameter.

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And you can use the NICE and RE-NICE commands to change process priorities.

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When cgroups are used, NICE values apply to processes with the same relative CPU weight.

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And the best practice, forget about NICE values.

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If you use cgroups, you use cgroups to define resource usage in general.

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And the only use case for the NICE value is where an individual user who is starting a

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heavy job can lower the priority of that heavy job.

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Let me demonstrate what may be going wrong on a system that is using NICE together with

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cgroups.

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So I'm going to leave my top window up and running.

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And I'm going to start my stress services units again.

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These were explained in a previous lesson.

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So systemctl start on stress1 as well as stress2.

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And we see them popping up in top.

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Now I'm going to top where I'm using R. R is a top interface where you can RE-NICE,

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right?

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So I'm going to RE-NICE 4824.

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And I'm going to RE-NICE it to a value of 15.

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So I'm seriously trying to make it NICE.

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Now what you should observe is the percentage CPU usage, the priority, as well as the NICE

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value.

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And what do we see?

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We see that the CPU usage doesn't change a thing.

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Priority has changed and the NICE value has changed, but it just doesn't apply because

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cgroups apply as well.

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And that's what you need to keep in mind when you are using NICE on a system that has cgroups.