AMD Ryzen 9 7950X P-State/CPUFreq Frequency Scaling Performance On Linux

[Anux]

[USER="26131"]
Also, it would be interesting to see if the Ryzen 9 7950x can be cooled by air in 105w and 65W "Eco mode".

No need for eco mode, just put the passive cooler on and it will automatically throttle to the coolers capabilities.

[coder]

No need for eco mode, just put the passive cooler on and it will automatically throttle to the coolers capabilities.

M@GOid didn't say "passive".

One question to answer would be how many Watts it reaches, with cooler X. That's essentially your experiment.

Another question would be whether "Eco mode" throttles it before it hits the thermal limit (using cooler X), in the two TDP settings specified. That won't necessarily follow from the first, but if we know how Eco mode behaves and what performance a given cooler delivers, then we can make some guesses.

[yump]

Schedutil whiffs again :-/

It's just depressing to see it flouder over and over while so many big players bypass the kernel frequency governor, either at a lower level like Intel HWP/AMD EPP, or userspace utilclamp on Android.

[g.maverick]

"Frankly I'd love to see more Linux distributions go the route of Intel's Clear Linux where the performance governor is used by default on desktops/servers and then sticking to schedutil for laptops/mobile systems by default."
I’m sorry but I disagree with you about this.
Both from an ecological and economical pow I would rather prefer that the default setting goes with the most efficient in terms of performance/energy used.
Then people (or smart OS) with performance or energy-saving needs may change the setting.
I guess there would be billions of desktops/servers which would uselessly waste energy if the performance governor is set by default.

[Nuc!eoN]

Now if amd could only fix its thermal blanket... I mean IHS design.

Do you think it's a coincidence that it looks like a virus?

[shmerl]

So does 7950X have MSR hardware or not? Do you see cppc in cpuinfo / lscpu?

[arQon]

I guess there would be billions of desktops/servers which would uselessly waste energy if the performance governor is set by default.

Then you would very likely be wrong with that guess, as has repeatedly been shown *countless* times. For any system under meaningful average load, it is very nearly *always* the case that completing the work as quickly as possible at a high power draw is more efficient than completing it more slowly - that is, over a longer period - at a lower power draw.

Of course, you could just be confused by the difference between "consumption" and "efficiency" (which is common), but either way you still don't really understand the situation. I don't know a good resource specifically for this, but I'd assume Gamer's Nexus has probably covered it at some point. Possibly one of the AFAP segments on LTT has.

Admittedly, Intel (and now AMD) are trying very hard to *change* this fact of life by drawing absolutely insane amounts of power under "boost" clocks in an attempt to win the Bigger Numbers game, but judging by the results in this article they're still not there yet.

[geearf]

Does it make sense to use PSTATE with a different CPU scheduler or are these things somewhat linked?

[coder]

Then you would very likely be wrong with that guess, as has repeatedly been shown *countless* times. For any system under meaningful average load, it is very nearly *always* the case that completing the work as quickly as possible at a high power draw is more efficient than completing it more slowly - that is, over a longer period - at a lower power draw.

I'm skeptical that's still true. Back when the "race-to-idle" approach was being trumpeted, CPUs were much more primitive in how they handled frequency-scaling.

For a more modern example, look at the Ryzen 7 5700X. It's quite simply a clock-limited 5800X. If you're right, then the 5800X should use less total energy across their multithreaded test suite, yet we see the stock 5700X using 8.7 kJ while the stock 5800X uses 10.0 kJ.

Source: https://www.techpowerup.com/review/a...-5700x/18.html
(scroll to bottom)

In fairness, the 5800X does use less energy for the single-threaded test, but they're measuring something different than what you're talking about. For that measurement to be directly comparable, they'd have to add in the idle power used by the 5800X system, during the additional time needed for the 5700X to complete. That would close much of the gap, and give the 5700X an even bigger lead in the multithreaded case.

Possibly one of the AFAP segments on LTT has.

Based on the sloppy experiment design & analysis I've seen in some LTT videos, I give them zero heed.

[g.maverick]

Then you would very likely be wrong with that guess, as has repeatedly been shown *countless* times. For any system under meaningful average load, it is very nearly *always* the case that completing the work as quickly as possible at a high power draw is more efficient than completing it more slowly - that is, over a longer period - at a lower power draw.

To be precise I also said:

I would rather prefer that the default setting goes with the most efficient in terms of performance/energy used.

I am not excluding by principle that the most efficient scheduler can be the performance governor (but I am skeptical) still the main difference is likely on what you are measuring.
- you may evaluate the necessary energy to complete a set of tasks
- you may evaluate the total energy used by a server during a period of time during a set of tasks

In the second case, you need also to take into account the sleep consumption (hopefully) and the idle/low-power mode consumption of the device sitting there doing nothing.
The second case, unfortunately, is a good model for a lot of servers and desktops in the office that and many of them do not have proper energy-saving mechanisms at the hardware or configuration level, so having a default setting at the level of the OS taking account of that, in my opinion, it is important.