Re: AMD, CPPC, etc

[me]
> > On my desktop system, using 0 ("auto") mode works quite well: the
> > system idles around 80 to 95 watts, and when building ports or
> > /usr/src with all 32 CPUs going, gets up to the 320-watt range, all
> > without any OS work required.

On Mon, May 25, 2026 at 8:34 AM Olivier Certner <olce@freebsd.org> wrote:
> What's the EPP value you are using?  The default of 0?

Yes, I haven't fiddled with any settings except desired_performance,
at this point.

> Now, the question is: Do you get the same performance with these
> more power-flexible settings compared to the driver's defaults ...

Hard to be sure. My wattage measurement is from a cheap power
meter that the machine is plugged into, and I'm not sure what to use
to measure actual performance on real workloads (I don't have a
nice reproducible setup for proper comparison).

To continue though:

> (which are desired performance set to maximum performance
> (which reported value do you see for that?)

There are 32 separate triples.  For example:

    dev.hwpstate_amd.0.desired_performance: 0
    dev.hwpstate_amd.0.maximum_performance: 206
    dev.hwpstate_amd.0.minimum_performance: 12

with the numbers going up to 31 (`sysctl -a` output
counts down from 31 to 0, which feels backwards, but
obviously it doesn't really matter). But each triple is
partly independent of the others, e.g.:

   dev.hwpstate_amd.3.desired_performance: 0
   dev.hwpstate_amd.3.maximum_performance: 211
   dev.hwpstate_amd.3.minimum_performance: 12

Oddly, writing to dev.hwpstate_amd.0.desired_performance
sets all 32 desired_performance values (to whatever value
I choose, even if it's above the reported maximum). I wonder
whether this would be the case on dual CPU-package systems
like a big EPYC setup.

The maximum "maximum_performance" value is 236 and
the minimum is 166 (device numbers 16 and 17), with most
of them clustered around 200-ish.

All of the "minimum_performance" values are 12.

> I suggest you forget about actual frequencies ...

Well, also they're mostly reported as high 5400-ish
when sampled, even with desired performance set to
auto. (Occasionally one will report closer to 5000.)
So they don't seem to be useful in practice.

Chris