AMD + Valve Working On New Linux CPU Performance Scaling Design

[illwieckz]

[…] we won't see the real performance gains we should be seeing.

Also one thing is that not everything is about performance. On my laptop with an Intel CPU I have to disable Intel pstate on kernel boot command line to get proper CPU scaling, otherwise the CPU is running at full performance like a rocket engine at takeof but running this way forever like if it had infinite fuel and there was no stage separation, trying to deliver from the hardware the very highest performance possible like if I was doing a drag race, and the laptop becomes super hot with the CPU never slowing down.

And that happens even on battery.

Sometime I just want to not have a brick of hot lava on my desk for hours, sometime I just want do not heat the room in summer, sometime I just want to have more than 15 minutes of autonomy on on battery, and sometime I just want my laptop to not die prematurely. Performance benchmarks do not draw such pictures.

[Linuxxx]

avg fps and even 1% low percentile don't show bad influence on frame time variance well enough. You will see MangoHUD's frame time graph to look bad with schedutil/powersave when under certain load conditions, causing stutter, missed vblanks etc. While schedutil is way better than intel_pstate powersave (why is this crap the default setting...), it is still not good enough.

While the performance CPU governor will undoubtedly always come out on top of schedutil under ideal conditions, with the Steam Deck being a handheld device this obviously can't apply here with both power as well as heat constraints.

Nevertheless, I think it would be interesting to see if simply disabling the boost clocks on the CPU and then comparing performance vs. schedutil would reveal any interesting insights...

However, at the end of the day, simply sticking with schedutil on any type of APU or SoC setup will probably be the ideal route going forward, as Android is already showing since a few years now.

[kiffmet]

Schedutil + ProjectC/PDS w/ Kernel 5.13 works pretty damn well on my 3900X. PDS does better what a part of what AMD's "suggested cores" CPPC feature tries to accomplish: Have threads from the same task share the same CCX/"L3 cache slice" if possible. This already resulted in a big performence improvement, esp. in gaming.

[intelfx]

Schedutil + ProjectC/PDS w/ Kernel 5.13 works pretty damn well on my 3900X. PDS does better what a part of what AMD's "suggested cores" CPPC feature tries to accomplish: Have threads from the same task share the same CCX/"L3 cache slice" if possible. This already resulted in a big performence improvement, esp. in gaming.

That's a totally different thing from what CPPC2/"preferred cores" is. It's about putting the most demanding task(s) onto the most performant core(s), and putting all the background tasks onto the least performant CCX (doesn't matter where, they're background).

[kiffmet]

intelfx except that on AMD CPUs CPPC2 reported "most performant cores" do not even correspond to the cores that can hit the highest peak&sustained frequencies. PDS without CPPC2 on Linux works consistently better than CPPC2 with the Windows scheduler and it can migrate background tasks to other CCXs aswell in case a task demands to utilize it fully.

[intelfx]

intelfx except that on AMD CPUs CPPC2 reported "most performant cores" do not even correspond to the cores that can hit the highest peak&sustained frequencies.

Can you back this up?

I owned two AMD CPUs of two different generations and it was true on both.

PDS without CPPC2 on Linux works consistently better than CPPC2 with the Windows scheduler and it can migrate background tasks to other CCXs aswell in case a task demands to utilize it fully.

It would be interesting to know how you managed to compare two schedulers in two different operating systems.

[azdaha]

This might be a stupid question altogether, but can anyone point out any benefit to owning a Zen1-based CPU?
The positive reception by consumers to that, arguably, led to the success of subsequent generations of the CPUs. But, if everyone was to hold out until Zen2 and later, would that make it more difficult to get those subsequent improvements?