Static Placement, Dynamic Issue (SPDI) Scheduling for EDGE Architectures

  • Authors:

  • Ramadass Nagarajan;Sundeep K. Kushwaha;Doug Burger;Kathryn S. McKinley;Calvin Lin;Stephen W. Keckler

  • Affiliations:

  • The University of Texas at Austin;The University of Texas at Austin;The University of Texas at Austin;The University of Texas at Austin;The University of Texas at Austin;The University of Texas at Austin

  • Venue:
  • Proceedings of the 13th International Conference on Parallel Architectures and Compilation Techniques
  • Year:
  • 2004

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Abstract

Technology trends present new challenges for processor architectures and their instruction schedulers. Growing transistor density will increase the number of execution units on a single chip, and decreasing wire transmission speeds will cause long and variable on-chip latencies. These trends will severely limit the two dominant conventional architectures: dynamic issue superscalars, and static placement and issue VLIWs. We present a new execution model in which the hardware and static scheduler instead work cooperatively, called Static Placement Dynamic Issue (SPDI). This paper focuses on the static instruction scheduler for SPDI. We identify and explore three issues SPDI schedulers must consider-locality, contention, and depth of speculation. We evaluate a range of SPDI scheduling algorithms executing on an Explicit Data Graph Execution (EDGE) architecture. We find that a surprisingly simple one achieves an average of 5.6 instructions-per-cycle (IPC) for SPEC2000 64-wide issue machine, and is within 80% of the performance without on-chip latencies. These results suggest that the compiler is effective at balancing on-chip latency and parallelism, and that the division of responsibilities between the compiler and the architecture is well suited to future systems.