PC "throttles" intermittently despite all software/hardware reading smooth, high framerate

[Narrlocke]

Hi.

I'm at a loss, I've had this issue for a long time and never been able to fix it.

I regularly switch my monitor/frame cap settings between 120hz and 144hz while testing this. Whenever I'm playing a game that relies on the framerate being smooth, I can visibly see it throttling down and dropping frames despite all software and hardware reporting perfect performance. Confusingly, everything runs perfectly fine for 10-60 seconds, and then visibly starts becoming choppy for 10-60 seconds, giving a "perceived" performance of 60hz to even 40hz. This happens both with 120/144fps games visibly throttling down to 60, and sometimes 60fps games visibly throttling down to something lower with a lot of dropped frames.

My hardware:
CPU: 9900k
GPU: Gigabyte Rtx 3080
Mobo: Asus prime z390-a
Monitor: AOC Q27G1wg4
PSU: 850w
RAM: Corsair dominator 3200mz 4x8gb

I've tried various combinations of Freesync on/off, V-sync (various types, with/without triple buffering)

I've tried several options on my monitor, MBR, Freesync and Overdrive options

I've tried overclocking my CPU and running it at the base clock speed

I've checked my GPU/CPU (individual core) utilization, nothing is hitting 100% (or even over 50% since I don't regularly play many demanding games) when this happens

I've checked my temperatures, usually nothing is over 65c when this happens.

I've ensured everything is running off of an SSD to prevent loading stutters.

I've tested with my primary monitor being the only one plugged into the system

I've updated all drivers, including flashing a new bios and reinstalling windows

The game I use to test solutions to this issue the most consistently is Overwatch since it's extremely visible and seems to happen consistently on that.
Can anyone teach me how to diagnose and fix this, please?

 

[Narrlocke]

If anyone finds this at another time, I either fixed or heavily mitigated the issue. I think it was a combination of Nvidia's driver framerate cap being very volatile (frame times rapidly flickering between 130-144+) causing vsync to completely trash my performance, I seem to have mostly worked it out by downloading RivaTuner and using their much more stable framerate cap combined with freesync.

 

[Mussels]

Another motherboard with terrible VRMs

Fixing the VRM thermals of the ASUS Prime Z390-A with a 40mm fan and 2 zip-ties. - YouTube
Fixing the VRM thermals of the ASUS Prime Z390-A with a 40mm fan and 2 zip-ties. : hardware (reddit.com)


From a forum thread over here

Question and answer about your motherboard

I have an Asus Prime z370-A motherboard and have just purchased a 9900KF processor. How risky would it be to run a 9900KF with that mobo?

Z370-A can probably draw 120A at MAX, under ideal temperature, probably 70C
For a 9900K/F under full AVX 5ghz it would probably be around 170-190A.

You'll be getting VRM throttling causing the CPU to "run cold", and differing workloads (from the CPU and GPU) producing more/less heat making the issue a bit erratic
Nvidias frame rate limiter is great, but vsync and FPS limits is a complicated topic that can vary per game - in your instance i'd say any limit that reduced CPU usage or heat in general, would help massively
(As i brought up recently elsewhere, an FPS cap at 60FPS has lower latency than a 120FPS setup with the GPU maxed out - and that's BEFORE any throttling occurs)