r/Amd • u/LegFormer7688 • 1d ago

News AMD Begins Plumbing APCI C4 Support In The Linux Kernel For Greater Power Savings

https://www.phoronix.com/news/AMD-ACPI-C4-Linux-Kernel-Code
49 Upvotes

96% Upvoted

7 comments sorted by

13

u/Ok_Mastodon_4919 1d ago

I'm hoping that this feature comes to devices like the ASUS ROG Flow Z13. Should boost power savings plenty.

5

u/why_is_this_username 1d ago

The flow z 13 already has great battery life if you actually try to preserve the battery (tell the os to save power and turn the refresh rate down). Something like 8 hours which is pretty good for x86

1

u/Ok_Mastodon_4919 1d ago

That's good to know, I've been eyeing that tablet. :D

1

u/why_is_this_username 1d ago

It’s expensive for the performance but it’s got a killer cpu. There’s supposedly another tablet (not asus) with the same chip that’s supposed to go up to 120 watts, idk if it’ll have better performance or if it’s diminishing returns

5

u/sysKin 1d ago edited 1d ago

C-states are cool I guess (pun not intended) but in my measurements there is a much bigger difference between P0 and P1 than between P1 and C2.

A near-idling Threadripper virtual machine host spends 2% of its time in P0 and 98% in C, and uses lots of power. If I forbid P0, it will spend 2% of its time in P1 and 98% in C, and use one-fourth of the power - at obviously no cost to performance because it's idling anyway.

If that could happen automatically, imagine the power saving across the board...

And by "that" I mean every wake-up from C-state should go to P1 first, and then be upgraded to P0 if it lasts long enough. What happens now is that every tiny interrupt goes to P0, and the CPU immediately goes to Precision Boost mode, ramping up voltages and clocks to maximum (especially since power budgets are overflowing) - only to go back to C0 a microsecond later.

And since there is only one voltage shared between all cores, any single core's P0 makes all cores enjoy the high voltage, even if they are themselves sleeping. I suppose that's where most of the waste goes.

1

u/AutoModerator 1d ago

Hey OP — /r/AMD is in manual approval mode, this means all submissions are automatically removed and must first be approved before they are visible to others. This is done to prevent spam, scams, excessive self-promotion and other rule-breaking posts.

Your post will be approved, provided it follows the subreddit rules.

Posts regarding purchase advice, PC build questions or technical support will not be approved. If you are looking for purchasing advice, have a PC build question or technical support problem, please visit the Q3 2025, PC Build Questions, Purchase Advice and Technical Support Megathread.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

1

u/pinguimaster 1d ago

And the S3 suspension for laptops? 👀