AMD P-State vs. ACPI CPUFreq Testing With Ryzen Laptops On Linux 5.17

[Anux]

I don't know too much how windows consider it "off" (they just doesn't appears, if I'm remembering well), but,

They don't appear in taskmanager? I have never seen that.

the lower I see with powertop is "C2" (more than 90% on powersave, which is fun, since there is 2% on C1, so, a huge part is missing, I guess it's C0), another fun part is whatever schedutils, conservative or powersave, the percentages in C1 and C2 are almost the same, only the frequencies looks just higher.

Shure the percentage is always the same, because the CPU only enters C-states if it is idling. Run something CPU intensive and see how C0 (thats CPU on with no power saving) gets 100%. To get deeper C-states you might need to enable them in BIOS, if your CPU supports them. Old core 2 duos already got up to C6 and modern CPUs might go to C10.

[Linuxxx]

Venemo

Still sure that Valve doesn't want to implement an easy toggle to switch over from schedutil to the performance governor for the public release of SteamOS 3.0?

And any guess why the Steam Deck still prefers acpi-cpufreq over amd-pstate, even though AMD & Valve publicly told pre-launch the latter was developed for better efficiency & performance, i.e. a better gaming experience?

[Michael]

It would have been useful if all the tests had performance per watt results, simply saying pstates + schedutil wasn't as fast doesn't really give the full picture especially when the percentage difference isn't that much but could make a difference in how long the battery lasts

Click on the OpenBenchmarking link at the end of the article for all the data... But basically included all the interesting ones in the article.

[PAUL007]

Will it support Ryzen 7 4800H Zen2 mobile ?, cant able to get p-state to work , my bios don't show cppc option.

[agd5f]

seems to be an artifact of the amd_pstate driver sometimes making bad decisions

The CPU frequency drivers don't actually make any decisions about what clocks to choose. They just provide the range of available performance levels. The governors actually pick the clocks based on what levels the CPU frequency drivers make available. I think part of the problem is that the frequency is not a good interface for performance. CPPC purposely uses abstract performance metrics rather than frequencies to define it's ranges. See section 8.4.5 of the ACPI 5.1 spec (https://uefi.org/sites/default/files...5_1release.pdf). Unfortunately, the governors are designed to work with all sorts of different CPU frequency drivers. For example, in most cases, it doesn't make sense to run the frequency lower than the max frequency allowed at the minimum voltage. Going below that doesn't really save much power, but does lower performance. In CPPC parlance, you would mainly want to stay within the range of "lowest nonlinear performance" and "nominal performance". I'm not sure that the governors take that into account when selecting a frequency. When setting up the legacy ACPI P-states, there are fewer frequencies to pick from, but I suspect most vendors map the lowest P-state to roughly the same target as the "lowest nonlinear performance" level from CPPC.

[loganj]

i thought that this amd thing was suppose to help playing games for longer period without CPU Throttling

[birdie]

For desktop Ryzen 5000 CPUs there are some bugs to be solved:

https://bugzilla.kernel.org/show_bug.cgi?id=215729

https://bugzilla.kernel.org/show_bug.cgi?id=215800

https://bugzilla.kernel.org/show_bug.cgi?id=215801

[skeevy420]

Venemo

Still sure that Valve doesn't want to implement an easy toggle to switch over from schedutil to the performance governor for the public release of SteamOS 3.0?

And any guess why the Steam Deck still prefers acpi-cpufreq over amd-pstate, even though AMD & Valve publicly told pre-launch the latter was developed for better efficiency & performance, i.e. a better gaming experience?

That's what I do. amd-pstate+ondemand for regular stuff, amd-pstate+performance via gamemode when gaming. Works great. I was upset that GE reverted the patch to Proton-GE that made it unnecessary to have to run gamemoderun last week.

I use ondemand because schedutil is a bit too aggressive in clocking down and I'm on a desktop.

[Soul_keeper]

With ondemand, amd-pstate seems to show the largest regression compared to cpufreq in my quick tests.
Some games are showing near 10% performance drops.

There is an benchmark tool called cpufreq-bench in the kernel for comparing the different governors also.
/usr/src/linux/tools/power/cpupower/bench/
I guess they use this as a quick run to test for obvious regressions.

[Venemo]

Venemo

Still sure that Valve doesn't want to implement an easy toggle to switch over from schedutil to the performance governor for the public release of SteamOS 3.0?

And any guess why the Steam Deck still prefers acpi-cpufreq over amd-pstate, even though AMD & Valve publicly told pre-launch the latter was developed for better efficiency & performance, i.e. a better gaming experience?

Sorry, I don't work on that stuff and don't have enough knowledge about this topic to give you a good answer.

My personal opinion is that I haven't seen much difference between various CPU governors on my own computer. Regarding the Deck, I trust that the people who work on it know what they are doing.