[Bug 217931] amd-pstate lacks crucial features: CPU frequency and boost control

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=217931

--- Comment #59 from Perry Yuan(AMD) (Perry.Yuan@amd.com) ---
(In reply to Artem S. Tashkinov from comment #56)
> Here's my report for 6.8.4 and Ryzen 7 7840HS:
> 
> 1. Setting scaling_max_freq works, cool, but you cannot go below 544MHz. You
> can set 400MHz but the CPU will continue to jump to 544MHz, not a big deal.
> 
> 2. Setting scaling_min_freq sort of works, the CPU _prefers_ to stay at this
> specified frequency but occasionally drops to 400MHz. Then, the CPU doesn't
> totally respect it, i.e. for values below 1.4GHz it stays around 1397MHz.
> The relationship is not linear, setting 4GHz results in the CPU preferring
> 3766Mhz. Or 2GHz -> 1982MHz. Not a big deal. Unlikely anyone would want to
> set the lowest frequency.
> 
> 3. /sys/devices/system/cpu/amd_pstate/cpb_boost is missing altogether:
> 
> # find /sys -iname '*boost*'
> [nothing]
> 
> So, my only remaining question is where's boost support? Or it's not
> supported for all Zen CPUs?
> 
> Thanks a lot for your work regardless!
1.  please try to apply the two patches for your cpb testing. 
https://lore.kernel.org/lkml/cover.1711335714.git.perry.yuan@amd.com/
https://lore.kernel.org/lkml/Zfqv3ckVU4km+RLr@BLR-5CG11610CF.amd.com/

2. are you testing under EPP driver mode? the 400MHz is the lowest freq,
however it dose not mean the CPU will be keeping at 400MHz, it will wake up and
idle and  bump up frequency shortly according to the workload.  you need to
know, when the Core is idle, kernel will not get the realtime frequency by
APERF/MPERF, cpufreq just show the lowest freq as 400MHz. It is not an issue. 

There is one idle frequency defined by power firmware, it is 1.4GHz for some
client system, the lowest active frequency is not 400MHz, it is 1.4GHz.  so you
have no need to worry the 1.4GHz or 400MHz, it is not a problem.

3. the invalid max frequency value issue is caused by wrong highest perf value
defined by pstate driver, I have been working a solution to fix that. with EPP
driver mode, it will not cause any performance problem, just a little
uncomfortable to see the wrong value listed.  

Perry.

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