Warp scheduler
Beginner
The part of a GPU core that decides, every tick of the clock, which team of workers gets to go next.
Novice
Hardware in each GPU core that, every clock cycle, picks one warp whose next instruction is ready and sends that instruction to the math or memory units.
Expert
One per SM quadrant on recent NVIDIA parts, one issue per cycle. Policies such as loose round-robin or greedy-then-oldest trade fairness, cache locality and how well warps stagger their long-latency stalls.
Explained in SIMT and GPUs (Architectures).
See also: Warp (wavefront), Latency hiding.