Re: kern/59932: Setting CPU frequencies on Zen 3 systems is problematic

["Emmanuel Nyarko via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/59932; it has been noted by GNATS.

From: Emmanuel Nyarko <emmankoko519%gmail.com@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: kern-bug-people%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost,
 netbsd-bugs%netbsd.org@localhost
Subject: Re: kern/59932: Setting CPU frequencies on Zen 3 systems is
 problematic
Date: Tue, 20 Jan 2026 14:35:43 +0000

 Hi,
 
 > On multiple Zen 3 systems (Ryzen 5500, 5700X):
 >=20
 > sysctl -a | grep freq
 > machdep.dmi.processor-frequency =3D 3400 MHz
 > machdep.tsc_freq =3D 3393633000
 > machdep.cpu.frequency.target =3D 3400
 > machdep.cpu.frequency.current =3D 3400
 > machdep.cpu.frequency.available =3D 3400 2800 2200
 >=20
 > Changing the frequency works. However, after setting frequency.target =
 to 3401 (which is 3400, with turbo clocking enabled, IIRC), all future =
 attempts to set the clock fail:
 >=20
 > sysctl -w machdep.cpu.frequency.target=3D3400
 > sysctl: machdep.cpu.frequency.target: Device not configured
 > sysctl -w machdep.cpu.frequency.target=3D2200
 > sysctl: machdep.cpu.frequency.target: Device not configured
 >=20
 > On each attempt to change CPU frequency, the kernel prints:
 >=20
 > [ 2823136.558871] acpicpu0: autoconfiguration error: failed to get =
 frequency (err 22)
 > [ 2823141.718910] acpicpu1: autoconfiguration error: failed to get =
 frequency (err 22)
 
 from source inspection, returning an EINVAL seems like this particular =
 machine uses a=20
 Fixed Hardware address space ACPI type and has no support for AMD =
 =E2=80=9CVID/FID=E2=80=9D algorithm=20
 for intermediate dynamic adjustments of Pstates. so it matches to an =
 invalid status address (0) for the unknown=20
 Pstate that you are trying to change to (3401).=20
 
 https://www.netbsd.org/docs/guide/en/chap-power.html
 
 you can =E2=80=9Cusually" verify that if your reported frequencies end =
 in 1. looks like this man page reveals a=20
 software layer aid to that but seems to be inneficient as compared to =
 hardware support.=20
 
 can you check dmesg to see if P state FIDVID flag is seen on acpicpu ? =
 and maybe compare to the other machines ?
 If it lacks the support, maybe you simply can=E2=80=99t do that due to =
 hardware limitation.
 
 NB: this is just by source inspection. hope it helps.
 
 
 
 Emmanuel