I forgot you were talking VR. Are you limiting your headset refresh rate?
I don’t know much about VR, but I noticed something the other day when trying with a Quest 2. I set the headset refresh to the minimum (I think 60Hz) from the start thinking my GPU wouldn’t run it well. I noticed that suddenly I’m main thread limited with very high CPU frame times even though I have a weak GPU when it comes to VR. I couldn’t figure out why that was so decided to increase the refresh rate of the Q2 and I noticed my CPU frame times went down and my overall fps went up.
My guess is that the artificial frame limit due to the refresh rate presented itself as a CPU limitation, like a pause instruction. For example, if the CPU can complete a frame in 10ms, but the frame rate is limited to every 33ms (30fps/60Hz VR), then there’s a 23ms period of sim inactivity that the CPU isn’t doing anything, which shows up as a 33ms total CPU frame time.
Like I said, I don’t know much in this area, but that’s my specific issue regarding abnormally high main thread frame times. Running at 90Hz basically fixed it for me.