Lessons learned from dataflow (Continued)
Microprocessors: Finding enough fine-grain parallelism to fully exploit the processor will be the main problem for future superscalars.
Solution: enlarge the instruction window to several hundred instruction slots; two draw-backs
- Most of the instructions in the window will be speculatively assigned with a very deep speculation level (today's depth is normally four at maximum). ? most of the instruction execution will be speculative. The principal problem here arises from the single instruction stream that feeds the instruction window.
- If the instruction window is enlarged, the updating of the instruction states in the slots and matching of executable instructions lead to more complex hardware logic in the issue stage of the pipeline thus limiting the cycle rate.