AMD P-State Preferred Core Support For Linux Tried A 13th Time

[phoronix]

Phoronix: AMD P-State Preferred Core Support For Linux Tried A 13th Time

One of the features sadly not having made it in time for the Linux v6.8 kernel merge window is the AMD P-State Preferred Core support. This is about being able to properly communicate to the kernel and scheduler about "preferred cores" such as cases of some CPU cores having higher maximum frequencies or better performance characteristics than others. This is becoming more important with AMD Ryzen processors beginning to see a combination of Zen 4 and Zen 4C cores and other cases like AMD 3D V-Cache enabled processors where some cores would be preferred over others for performance sensitive work...

https://www.phoronix.com/news/AMD-P-State-Preferred-Core-13

[Kjell]

I experienced a lot of lag spiks after enabling CPPC Preferred Cores option in BIOS and adding kernel parameter amd_prefcore=enable.

This happened with various games like Halo Infinite as well as in my Sway desktop with applications like VSCodium. I think the culprit is that there's already minor stuttering during shader compilation and using preferred cores made the lag more intensive.

For reference, I'm using 5950X + 6800XT and also amd_pstate=passive amd_pstate.shared_mem=1

I've tried this with 2 motherboards, ASUS X570-E & AUROS X570 I WIFI (mini).

Yes fTPM is disabled

[MastaG]

Unfortunately the pstate driver doesn't seem compatible with the zen2 3000 series Threadrippers.

https://bugzilla.kernel.org/show_bug.cgi?id=218171

Somehow my Asus motherboard is not exposing the correct cpu bit and ACPTI table information.

[post-factum]

amd_pstate.shared_mem=1

FWIW, there's no such option with the latest patchset iterations. Shared memory applicability is judged by a presence of

X86_FEATURE_CPPC

instead.

"adding kernel parameter amd_prefcore=enable" is not needed as well as this feature is enabled by default.

[jeisom]

I experienced a lot of lag spiks after enabling CPPC Preferred Cores option in BIOS and adding kernel parameter amd_prefcore=enable.

This happened with various games like Halo Infinite as well as in my Sway desktop with applications like VSCodium. I think the culprit is that there's already minor stuttering during shader compilation and using preferred cores made the lag more intensive.

For reference, I'm using 5950X + 6800XT and also amd_pstate=passive amd_pstate.shared_mem=1

I've tried this with 2 motherboards, ASUS X570-E & AUROS X570 I WIFI (mini).

Yes fTPM is disabled

I experienced issues when I tried to enable it initially, but those issues were resolved by bios updates, I believe, on my 5900x. You might see if there are any updates for your board and test again. YMMV though. Mine is an Asrock board.

[aufkrawall]

Great. And since it wasn't mentioned on this site already, I guess Intel cluster scheduling also once again has missed the window. That stinks...

[MastaG]

Oh well, then for 6.9 this summer we'll hopefully have this + intel cluster scheduling + all of the color bits in place for proper HDR support.

[toughy]

13th time is not a charm, apparently.

I would like to use preferred core feature, since I have 24 of them on my Threadripper 2000, and I suppose the best one out of 24 would stand out quite a bit.

But I just can't care much about this not getting through when AMD did worse things like when they discontinued development for Vega iGPUs, when those are still selling at retailers.

[agd5f]

But I just can't care much about this not getting through when AMD did worse things like when they discontinued development for Vega iGPUs, when those are still selling at retailers.

Realistically, nothing changes. Vega chips are ~8 years old at this point. Beyond bug fixes there have not been any major vega changes in years. On the Linux side, the drivers are open source and nothing really changes. On the windows side, drivers for older chips like vega come from a stable, bug-fix only branch and newer chips come from the mainline branch.

[Kjell]

I experienced issues when I tried to enable it initially, but those issues were resolved by bios updates, I believe, on my 5900x. You might see if there are any updates for your board and test again. YMMV though. Mine is an Asrock board.

Both motherboards had the latest BIOS revision :/

Just to clarify, the lag spikes in my system aren't the same which X3D users are complaning about. For example, common issue with Preferred Cores + X3D cpu are intermittent lag spikes which lasts 1 second. In my case (with a non-X3D cpu) it's only making microstuttering more apparent. If I had to guess, preferred core logic might be shuffling the game's logic from cores in one CCX to another CCX which is known to introduce latency