[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 #11 from Conrad Meyer <cem at freebsd.org> ---
Very interesting, thanks!  It's the low bits of 0xc0010061 following 0xc0010062
up that is surprising / causing hwpstate(4) to ignore the user's supplied
configuration (side note: we should really produce at least a *debug* log
message when we ignore the user-supplied P-state!).  I don't have an
explanation for why 0xc0010061 low bits are following 0xc0010062.  Nothing in
the kernel writes that MSR, as far as I can tell.

The documentation I have for c0010061 says it's error-on-write.  But it also
suggests that the value may be changed: "Attempts to change the CurPstateLimit
to a value greater (lower performance) than PStateCurLim[PstateMaxVal] leaves
CurPstateLimit unchanged.")  So I'm not really sure if software/firmware can
write it.  Maybe the CPU's power-governor is misconfigured and is attempting to
limit itself?  I don't have any explanation for why it would "follow" c0010062
stepwise, though.  Any chance other people with the same motherboard have
reported similar problems with Linux/Windows?  Any chance there is a BIOS
update available?

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