Criticality of optimization on GPU is very different than for CPU due to the extremely high performance contrasts. GPUs have "fast paths": Unintuitive depressing 1000x slowdown as compared to expectations or after a small change are often met when programming. Conversely, knowing these fast paths can lead to more than 1000x speedup. G80 series can be even less intuitive regarding this issue since it can very efficiently hide some unoptimalities (via threading) up to the point where suddenly it can no longer. To find and remain in these fast paths, it is important to understand how the GPUs work and behave. In particular, we were interested in how fragments are scheduled among G80 stream processors.