EDIT: Looks like some of my bugs were caused by HWiNFO running. Having HWiNFO running and changing voltages and/or timings in Wattman triggers some weird memory bandwidth bug. I have to do more tests to be certain.
The bugs concerning the ~210 GBytes/s to ~193 GBytes/s and reverting voltages still stand.
Tested hardware: Sapphire Nitro+ RX580 4GB / Windows 10 64bit (19.5.2. and 19.8.1. drivers)
ASUS P8P67 LE / i5 2500
8GB RAM
Tool used: poclmembench (GitHub - kruzer/poclmembench: calculates your gpu memory speed)
I have a custom Wattman profile:
This profile does not survive a computer's sleep mode. Even when I stopped using the sleep mode, sometimes the profile still gets bugged. My custom profile is stable, this still happens even if I increase the voltages slightly above default values.
What happens with my profile is this:
This brings me to memory timings and memory bandwidth.
Number 1. is my normal, default memory bandwidth/speed. Number 2. is a bug that happens when I change a voltage of any power state (it doesn't matter if I increase or decrease the voltage).
This isn't a bug in the poclmembench; slight decrease in performance can be observed in games. Restarting the PC is the only solution I know of to get the full ~173 GByte/s speed back, keeping your custom voltages as well.
Let's jump to memory OC.
When I OC my memory from 1750MHz to 2000MHz and change memory timings to level 1, I should get ~210 GByte/s, but this doesn't work most of the times. Often changing memory timings does not improve performance at all, due to a bug in Wattman. It doesn't matter if you have your timings set to automatic, level 1 or level 2; bandwidth won't change. This doesn't happen all the time, often you will get a bandwidth increase, but it's lower than it should be. Sometimes I only get ~183 GByte/s with the same settings when I should get ~210 GByte/s.
When the OC works as intended and I get my ~210 GByte/s, after restarting the PC the OC is broken and I get ~195 GByte/s. As shown on this screenshot:
I believe this is not intended at all. Way back with older driver (I can't remember the version anymore) I was able to keep my ~210 GByte/s OC even after PC restart/shutdown, but now it gets completely broken and goes down to ~195 GByte/s.
This nasty bug happened when I hit the "Reset" button in Wattman to revert to default settings (once I even got ~53 GByte/s and performance was very low in games):
As you see memory speed went completely down and gaming performance was affected quite a bit... Again I had to restart my PC to get the default ~173 GByte/s.
You may not have these bugs, but I do on my RX580.
Drivers were reinstalled using DDU as well, I even disabled Windows 10's fast startup feature as recommended on AMD forum.
I hope you can test this as well and report this to AMD too.
The loss of performance is not caused by improper adjustment of WattMan settings. You are trying to make changes to WattMan settings without resetting (to WattMan not the PC). WattMan is insufficient. It also changes core clock speeds and voltages without crash. When Windows Power Options turned off the display, it either does not wake up or WattMan makes an error. I think they can't fix these problems. There have been similar problems for years.