kernel 4.3.0-rc0 (Fedora snapshot)
mesa git master / with also experimental radeonsi shader cache (still stalls
with it even)
LLVM trunk (Sept 10th, 2015 build)

I've done some profiling of Borderlands 2 (just the menu intro) and discovered
what may be causing the stalls.

Apitrace: https://drive.google.com/open?id=0Bze7CJKD12nORWQ4RTdIbk4zT1k

Results from profile show the following calls with spikes:

25208614 [glDrawRangeElements]
25208651 [glLinkProgram]
29526799 [glDrawRangeElements]
29526657 [glDrawRangeElements]