Performance drops after some time, KDE5 and Unity.

I’ve had this issue for the first time ~2 months ago. It was happening on KDE5 desktop on Arch. I thought that it’s problem with their compositor and moved back to KDE 4. It was ok there, it was occuring on XFCE too.

About 2 weeks ago I installed Unity on Arch, since then I have same issue as with KDE 5. Performance of TF2 drops from 80-120 fps to 17-30.

I did some tests and I saw one thing happening everytime something pulls handbrake on my GPU.

“PCIe Bandwidth Utilization” when minimized TF2 is in main menu is normally at ~17%, when problem occurs it’s at ~30%.

When I’m in MP on map pl_frontier_final minimized, bandwidth is around 1%, when problem occurs it’s ~56%.

Also, VRAM usage is up to 100MB higher when it occurs.

One last thing, when I leave game, I can’t logout with logout button, only “killall -u user” works. If I switch tty to for example 2 and back to 7 compiz crashes.

Specs:

ASUS GTX 550 Ti 1GB
Core i3 2100
8GB DDR3 @ 1333 MHz
Arch x64
Unity
Nvidia 346.47

Edit.

I forgot to add, not only frame drops but also stuttering occurs.
nvidia-bug-report.log.old.gz (90.8 KB)
glxinfo.txt (64.8 KB)

Same problem on Ubuntu 15.04 AMD64 with Nvidia 349.12 driver. Frames drop to below 30 and it’s stutter fest.

How can I pinpoint this issue ?
As I said earlier, if I logout it runs fine.
nvidia-bug-report.log.gz (95 KB)

@PootisMan:

Erm, have you considered the obvious problem of overheating?
No disrespect, I was tracking similar regression for few hours when I noticed that inspite of fan turning at maximum speed, litle air was getting trough (dust filter protecting got stuffed with dust).
Coincidentally I noticed the thing right after updating drivers, so I went on wild goosechase.

When the thing gets too hot, frequencies drop and if it doesn’t help, throttling occurs.

Yeah, sure. Second gen Fermi GPU has problems with heat… It’s not AMD 290X with stock cooler. Besides, I’m cleaning it every ~ 4 months. And I have played GTA IV yesterday. It’s normal for it to hit 86 degrees, but it won’t go further.
It’s CPU limited in TF2 because it’s noisy as hell in GTA.
It feels like some sort of leak, I can use it in desktop mode for few hours, but then there’s high chance it will suffer from low framerate and stuttering.