[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 #9 from Conrad Meyer <cem at freebsd.org> ---
Another test to try (maybe after entering a non-P0 p-state, not sure if that
matters) if you'd like:

$ cpucontrol -m '0xc0010061' /dev/cpuctl0

This is the PStateCurLim register, and the low 3 bits are 'CurPstateLimit'.  It
represents the highest performance P-state the processor is (currently) allowed
to enter.  I don't know why it would be non-zero if the processor is in P0 at
boot, but I suppose it could be a BIOS issue.

Finally, you could try just manually checking the last set P-state:

$ cpucontrol -m '0xc0010062' /dev/cpuctl0

(Last-set P-state is the low 3 bits of that register.)  Or setting P-state 0
across all cpus manually, bypassing hwpstate(4):

$ for i in $(jot 16 0) ; do cpucontrol -m '0xc0010062=0x0' /dev/cpuctl$i ; done

(Bourne sh; I don't know if that works in csh or anything exotic.)

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