AMD Ryzen 9 3900XT CPUFreq Governor Comparison With Linux 5.9

[brent]

Yeah, we really need a better CPU governor. Unfortunately, AMD's CPPC2 special governor (similar to intel_pstate) was rejected. CPPC2 always the CPU to ramp up faster and react quicker to load changes because the p-state control is fully handed to the CPU and independent from the OS. The OS then only configures and monitors the p-states.

At the time, it was rejected because maintainers apparently didn't want yet another vendor specific governor. That seemed unfair to me at the time. We're still waiting for a generic CPPC2 driver...

[s_j_newbury]

I don't think most comments or indeed Michael are getting the point of cpu frequency governing. It isn't supposed to, and cannot increase sustained peak performance, which is actually what the performance governor does: Set CPU speed to the maximum non-turbo pstate within scaling range and leave it there. Turbo states will activate unless explicitly disabled. It's the opposite to 'powersave'.

The idea of not using 'performance' is to reduce power consumption, and hence heat dissapation. This can allow for higher burst peak performance as a side effect since the margin is greater to ramp to turbo states, but transition latency means cycles are missed as demand increases.

'Schedutil' is supposed to address the issue of latency along with improving decision making when not to ramp up by anticipation of future performance through better information. 'ondemand' is always behind.

[leipero]

s_j_newbury I'm kinda confused about the role of the governors, on my system, it seems they do not play any role whatsoever (I did not do extensive testing tho.). In the past, I would usually set CPU to the max frequency, disable turbo, undervolt it and be done with it, so in that scenario it makes sense that governors are irelevant.
Now, since my motherboard doesn't support undervolting for specific "APU" i use, I do not do that, even tho. most of the power saving options are disabled in UEFI (I think), CPU still scales with frequency and I've experimented with governors as well, and it seems they do not make any difference, CPU would always scale, even with "performance" governor.

For example, at the moment I do not have any governor and module loaded on my system, and CPU/iGPU still scales properly, even with all options disabled in UEFI. Maybe "APUs" work differently with power management in comparison to the "classic CPUs"? All I really do is disable turbo since it produces more heat for very little to no benefits at all, and overvolts CPU to the point I do not feel comfortable with.

[pmorph]

I'd like a governor that works more like a screensaver. I.e. one that tunes things down only if there hasn't been much to do for like forever (since several seconds, or tens of seconds). Not sure if this is possible to do by adjusting parameters. I did try playing with them several years back, but results were not too great.

[torsionbar28]

I don't think most comments or indeed Michael are getting the point of cpu frequency governing. It isn't supposed to, and cannot increase sustained peak performance, which is actually what the performance governor does: Set CPU speed to the maximum non-turbo pstate within scaling range and leave it there. Turbo states will activate unless explicitly disabled. It's the opposite to 'powersave'.

The idea of not using 'performance' is to reduce power consumption, and hence heat dissapation. This can allow for higher burst peak performance as a side effect since the margin is greater to ramp to turbo states, but transition latency means cycles are missed as demand increases.

'Schedutil' is supposed to address the issue of latency along with improving decision making when not to ramp up by anticipation of future performance through better information. 'ondemand' is always behind.

Was kind of thinking the same, the various governors are not designed to compete with one another - they are complementary. You select the one that is most appropriate for your use case. I.e. the one that delivers the required level of performance with the lowest power consumption / heat dissipation.

[torsionbar28]

I'd like a governor that works more like a screensaver. I.e. one that tunes things down only if there hasn't been much to do for like forever (since several seconds, or tens of seconds). Not sure if this is possible to do by adjusting parameters. I did try playing with them several years back, but results were not too great.

Same here, I ended up using crontab entries. Performance during the range of known peak hours, and Powersave at all other times.