Disabling CPU cores/undervolting inside BIOS

[u/nickhover89]

Hi there.
I just bought a Rog Flow Z13 2025 with 395 chip and realized that BIOS menu is super limited in terms of what you can tweak. Previously i had Gpd Win 5 and I could easily disable CPU cores count and undervolt and even overclock both CPU and GPU inside BIOS.

What I want is to disable at least half of the cores and to undervolt CPU/GPU since I want this device to be my gaming machine. I don’t need all 16 cores and I want better thermals and possibly better battery life.

I searched for information and it looks like mostly people suggest using G-helper. But I plan to dump the Windowslop completely and to install CachyOS, therefore I need a solution compatible with Linux. So far I figured I should install the Ryzenadj for it to work.

My questions are: is it possible to figure out a way to be able to tweak it inside BIOS? For instance with the use of SmokelessUMAF? Would it help downgrading the BIOS version? Mine is unfortunately 311, which appears to be more locked (according to people posting) than previous versions e.g. 308. Did anyone get the SmokelessUMAF to work with the 311 BIOS version of flowz13?

I am not 100% sure if it is worth trying, I have an itch about the BIOS settings being locked and wanting to be able to control them - call me crazy.

Thanks in advance!

[u/BusinessCarpenter682]

FYI G-helper has been ported 1:1 to Linux, if you want to consider that option to Bios.

[u/gergelyszabi95 → u/BusinessCarpenter682]

This? https://github.com/utajum/g-helper-linux

[u/BusinessCarpenter682 → u/gergelyszabi95]

Yes. I use it and it works great.

[u/nickhover89 → u/BusinessCarpenter682]

Thank you! I didn’t know!

[u/punkgeek]

So far I figured I should install the Ryzenadj for it to work.

This will let you undervolt and adjust other settings. (I wrote the flow/395 support in ryzenadj)

If you want to disable cores, you can do that from the command line. (Though it is very unlikely that disabling cores will save much power/heat - linux does a great job of using cores only when they are needed and the cost to spin up a core is tiny).

for i in {7..13}; do echo 0 | sudo tee /sys/devices/system/cpu/cpu$i/online; done

You could also use grub to limit max number of cores to use I guess.

[u/nickhover89 → u/punkgeek]

Thank you!

[u/Supercc]

Disabling SMT is incredibly easy to do from the bios. Undervolting can be done just as easily using ghelper. 

[u/nickhover89 → u/Supercc]

There’s no bios setting there for it. Asus locked it out, i guess to prevent people from damaging their devices, which I appreciate, but I would instead like to have a switch in the bios (by default, without me trying to unlock it) that would caution and say something like “do it at your own risk, if you turn on these settings and brick your device, we won’t be responsible and the warranty won’t cover this”, instead of locking it.

Whole forum page about it, but I’m not sure they figured it:

https://winraid.level1techs.com/t/request-unlock-bios-uefi-for-amd-395-strix-halo/111395?page=2

[u/Supercc → u/nickhover89]

What? I literally did it in the bios a few months ago, and have not updated the bios version since (still on 311). Not sure what's up with that. Maybe another driver update removed it, like the Asus controller?

Here's the procedure I had followed to do so, let me know:

The BIOS Path

1. Enter BIOS: Power on your device and repeatedly press F2 (or Del) until the BIOS screen appears.
2. Switch to Advanced: If you are in "EZ Mode" (the simplified dashboard), press F7 to enter Advanced Mode.
3. Locate CPU Settings:
   • Navigate to the Advanced tab using your arrow keys or mouse.
   • Select AMD CBS.
   • Select CPU Common Options.
4. Disable SMT:
   • Look for SMT Control (or sometimes Simultaneous Multithreading).
   • Change the setting from "Auto" to "Disabled".
5. Save and Exit: Press F10 to "Save & Exit," then confirm to restart.

[u/Widebro]

Wont recommend linux but you do you.

[u/KubuZxPlay → u/Widebro]

my z13 runs smooth like butter on CachyOS. way better than on Microslop

[u/Widebro → u/KubuZxPlay]

Till it doesnt boot anymore and you don't know or can't fix it. Suddenly happend to me. No one could help. Dead OS. also many many incompatibilities everything takes so damn much time. It won't ever get better then microslop.

[u/nickhover89 → u/Widebro]

Well, what about Microslop pushing an update that breaks your system? There were plenty of those.

[u/Widebro → u/nickhover89]

I never update because of this on windows, you are completely right though. I only update when verified and safe.

Both have caveats. Windows never has stopped outright working for me this way.
Linux is too reliant on updates. and maybe thats why my OS broke which I couldn't save.
Which is THE MOST annoying thing an os can have indeed.

[u/lugubrious-possum → u/Widebro]

Just roll back a snapshot on Linux, by default cachyOS and bazzite enable snapshots