[Bug 234733] Setting CPU frequency with sysctl dev.cpu.0.fr slows a Ryzen 2700X down

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=234733

--- Comment #18 from Conrad Meyer <cem at freebsd.org> ---
(In reply to sigsys from comment #15)
> It would already be pretty good if the kernel could detect the situation by
> double checking on one of those registers and log a warning.  Assuming it
> wouldn't risk causing even more problems on some other systems.

We used to verify set P-state on all cpus prior to r326383.  It gets pretty
inefficient to check all cores.  Checking just one only tells you one made it
to the configured P-state.  (AMD P-states are independent across each core; SMT
threads share a P-state domain.)

But that's not really the situation here; here we're restricting P-state
ourselves in software due to the (seemingly bogus) c0010061 limit.  In this
case, I added a debug log in the commit referenced in comment #17.

I am curious if Linux does any better.  Maybe they just ignore c0010061.

(In reply to sigsys from comment #16)
That's unfortunate :-(.

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