Hacking the schedutil governor to upshift to maximum clock rate at every process dispatch.

Valdis Kl=?utf-8?Q?=c4=93?=tnieks valdis.kletnieks at vt.edu
Thu May 26 10:20:16 EDT 2022

On Mon, 23 May 2022 17:37:09 +0300, David Kra said:

> I am considering modifying the scheduler and governor to get a jackrabbit
> start whenever a process is dispatched. Before learning how to, I would
> like some advice on whether to, and how much to do.

Step 0: gather actual data, and see if you will get any significant observable boost.

(If you don't know how to test if you will get any improvement,  you probably don't
know how to test for improvement after the patch is done.  So you may as well do
that part up front, unglamorous as it may be)

Hint:  powertop is your friend (or are the cool kids using something else this week?)

> * Is there a better way to achieve the same result?

It would probably be a lot easier to just set the CPU governor to "performance" mode.

> * Is this a dumb thing to do?
Probably, but it will depend on your use case.

> * Is it safe to rely on the existing code, firmware, and microcode to handle the
>  subsequent downclocking, and for my hack to only do the upclocking?

Well, you're just going to turn around and upclock it at the end of that process's
tiimeslice, so it's unclear what real benefit you'd get from downclocking.

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