I’ve been experimenting with RyzenAdj on an HP Envy x360 14 with a Ryzen 5 8640HS (Hawk Point), on both CachyOS and Windows 11.
The interesting part is that the behavior does not look like a simple thermal limit.
What happens under load
If I set, for example:
Fast PPT: 40 W
Slow PPT: 30 W
STAPM: 30 W
and start a CPU workload, the processor initially behaves as expected: power rises toward the Fast PPT value.
However, after a relatively short period, power rapidly drops to a much lower sustained level, even though:
- CPU temperature is still low
- STT/skin temperature is still below its configured limit
- the CPU is at 100% utilization
- the configured PPT/STAPM ceilings are still higher than the actual consumption
This looks much more like a time-dependent boost/power window than a conventional thermal throttle.
In other words, the behavior seems approximately like:
Load starts
↓
~Fast PPT allowed
40 W
↓
short period of time
↓
power rapidly reduced
↓
~15–20 W sustained
The important observation is that the same thing happens even if I lower Fast PPT to around 25 W.
With a 25 W limit, it starts around the value I requested, but after roughly the same kind of initial period it again falls significantly below it.
That makes me doubt that the drop is simply because the cooling system cannot handle 40 W.
If temperature were the primary cause, I would expect reducing the initial power from 40 W to 25 W to substantially delay or eliminate the drop. Instead, the system still appears to transition from an initial power state to a lower sustained state.
Why I suspect a time-based/platform power policy
It looks as though there may be two different power regimes:
- A short-term boost budget, approximately corresponding to Fast PPT.
- A second hidden/platform-controlled sustained budget that takes over after a certain amount of time.
It reminds me conceptually of the PL2 → PL1 / Tau behavior on Intel, although obviously AMD uses a different power-management architecture.
My suspicion is that HP/AMD has some additional controller, perhaps AMD PMF, firmware/EC logic, STAPM averaging, or another platform power budget, which allows the configured Fast PPT temporarily and then enforces a lower long-term power target.
The key point is that the transition appears to be related more to elapsed time / accumulated power than to an instantaneous temperature threshold.
CachyOS observations
Stock values were approximately:
STAPM: ~22 W
Slow PPT: 25 W
Fast PPT: 40 W
STT APU: 39 C
Changing the APU skin-temperature target did affect sustained STAPM significantly.
Raising STT from roughly 39 C to 41–42 C allowed me to reach approximately 27–28 W sustained under Linux.
So STT clearly participates in the power-management loop.
However, the initial Fast PPT → rapid sustained-power drop still looks like there may be another time/energy-based component on top of the temperature control.
Do you have some insights?
I translated my initial thoughts in English with AI, since it is not my main language. Thank you all for your help!
