TLDR: Was having big problems with 13900KS performance and smoothness due to PCIE ASPM being enabled in BIOS.
I have noticed that my brand new 13900KS, that is set to 5.6Ghz / 4.9 @ -100mV offset and was having very variable performance in some low threaded tests.
MicrobenchmarkGui latency was all over the place for same size, Aida was crazy, MLC was not loving me.
Also, package power at idle, with all C-States enabled was like 20W. I have started my investigation from this power -> after some digging, i have noticed that monitoring programs like MSI AfterBurner and HWInfo have quite high CPU load, then in ThrottleStop i have found that one of my cores is never really entering low power states.
It made little sense, so i have worked in BIOS, resettting, reaplying my OC with no results.
The power breakthrough came when I tested "Power saver" power plan. Package Power went down to to 7W at idle and benchmarks were much improved.
It made little sense, in MicrobenchmarkGui (large pages) i was getting perfect latency stair with power saver, but as soon as i enabled High Performance plan, it was bad again.
After resetting power plans in WIndows, some more toying, i realized -> HWInfo and Afterburner must be very busy with something, and in HP plan they are polling CPU non stop, while PowerSaver is probably tuning them down.
With this "discovery" i was finally on track to solving it: HWInfo64 has column - "Profiling Time" that can be enabled in settings and it was showing crazy times, like 500+ for my 3090:
I knew something was very wrong and suspected ASPM being enabled -> after trip to BIOS and disabling it, everything went back to normal, benchmarks have rock stable scores, package power when idle is <3W and cores are properly sleeping now as it should be:
So if anyone is having strange trouble, it might be worth visiting BIOS and checking ASPM settings, on idle system Hwinfo profiling should be real fast for anything not connected via USB.