Hi Doug!
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3- Dave/Darius - I am afraid to turn off power management after reading the warnings in the ACPI docs - which basically say thermals may become a problem if you mess with power settings. I did download the ACPI sdk and look through the documentation and I didn't see any function that seemed to address turning on or off processors. But I might have missed something.
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I suspect, like Darius, that either the processors aren't getting turned off, or something is turning them back on. This appears to happen on both Ryzen and Intel processors. One using SNAP and the other using Panaroma.
From a 'good to know how to configure this' perspective the easiest way to TEST this on your machine is to DISABLE the ACPI PowerManager (as per the note that Dave posted, see acpid.cfg file). I believe ACPI daemon dynamically picks this up, so no reboot is necessary.
Then you can shut OFF the cores you do not need running and test your WIN-OS/2 use.
If this work, you know precisely HOW to get this working when you need it working. After all, re-enabling the ACPI PowerManager is just as easy as disabling it. You could literally have a little pm_off.cmd & pm_on.cmd scripts that simply replace the appropriate acpid.cfg files, which ACPI PM then recognizes.
In my experience the big CPU temperature spikes only occur when you really start pushing the machine. We are talking here heavy FLOAT ops such as running the SYSBENCH FLOAT benchmark, etc.
For example: as I play around with this stuff on my end I find that the 48C idle temp of my AMD FX-8370 CPU (8 core, 5GHz) goes up to 51C...which is a pretty tiny amount of just 3C increase. But make note that this is only achieved by deploying the Noctua NH-15D CPU cooler, which is very much in the realm of the overclocking domain.
Prior to installing this cooler I was running a Corsair A70 setup, which was showing 55C at idle and when running the SYSBENCH FLOAT tests the temp would spike all the way to 64C. Heck, a couple of times (as I was screwing around with both CPU frequency and core voltage) I actually had the whole box automatically shut-down.
Soooo....with today's systems there is a good amount of protection built-in...but it's always good to review your specific specs to know exactly what your MAX values are.
Ultimately the experimentation is what will give you the true answers.
EDIT
====HERE (
https://man.netbsd.org/acpicpu.4) is a good summary of all of these C/P/T-states, how they relate to each other, etc.