This has been rattling around in my brain since the complaints of stutters and general performance drops began after the update. I have just done a bunch of digging and maybe someone with more experience with the DXGI can wade in here.
It seems that the SwapBuffers call can cause a significant latency in the runtime when combined with certain GPU drivers. I have seen anything from 100ms up to 2 sec pauses in getting a response from the dll. These issues go all the way back to early WDDM drivers (2.0 - up).
Is it possible we are seeing something similar here?
Edit:
The more I think about this the more reasonable it starts to sound. The fact that most users with this affliction have noted a significant drop in both CPU and GPU activity during the stutters would indicate that the program is waiting for something to happen. When the swapBuffers bug occurs the runtime seems to just nod off for a moment. Request goes in… dead air… response comes back and all continues as normal.