Date: Mon, 25 May 2026 20:23:57 -0700 From: Chris Torek <chris.torek@gmail.com> To: Olivier Certner <olce@freebsd.org> Cc: Warner Losh <imp@bsdimp.com>, Adrian Chadd <adrian@freebsd.org>, freebsd-current <freebsd-current@freebsd.org>, ShengYi Hung <aokblast@freebsd.org> Subject: Re: AMD, CPPC, etc Message-ID: <CAPx1GvfRJfnM4GKerD9i9fsHZ_9MY8R-xT-JKXFosJka4UiLig@mail.gmail.com> In-Reply-To: <11798552.X2hNYcAVgp@ravel> References: <CAPx1GvfaDdmj0vkzzinyhGm2mQRKgmOh3fpNXo-cgznoujVY-Q@mail.gmail.com> <CANCZdfoyqdEr_1%2Bkmi5_0TTG0VaAZMjXgGOubWt5nVK8aqe9DQ@mail.gmail.com> <CAPx1GvdM3yUK9vpTLYwE4yXm7R0Vzea96xAsPPrNZmEHqeb8-Q@mail.gmail.com> <11798552.X2hNYcAVgp@ravel>
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[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
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