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

[bugzilla-noreply at freebsd.org]

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

--- Comment #21 from Conrad Meyer <cem at freebsd.org> ---
(In reply to sigsys from comment #20)
c0010061 doesn't follow c00l0062 on my Zen1 + ASRock X370 system, for example.
:-)  Maybe it's a Zen+ thing, maybe it's a BIOS thing, who knows.

In any case I agree we don't really understand what it does.  It doesn't seem
to line up with the documentation, and I don't expect ignoring it to be harmful
to modern AMD hardware for power/thermal reasons.  (I expect HW made in the
last ten years to thermal throttle regardless of SW-set P-state.  My concern
around removing it entirely, as Linux seems to, is mostly that doing so might
be harmful for the older CPUs this driver supports (k10, k11).  But -- clearly
not a problem for Linux.)

I like your suggestion of a sysctl/tunable.  I propose defaulting to "ignore
c0010061."   I am having trouble coming up with an accurate and descriptive
docstring, though.  "If set, limit requested P-states to MSR c0010061[0:2]"
isn't exactly useful to end users, probably.

-- 
You are receiving this mail because:
You are the assignee for the bug.