Tasking with out-of-order spawn in TLS chip multiprocessors: microarchitecture and compilation

  • Authors:

  • Jose Renau;James Tuck;Wei Liu;Luis Ceze;Karin Strauss;Josep Torrellas

  • Affiliations:

  • University of California, Santa Cruz;University of Illinois at Urbana-Champaign;University of Illinois at Urbana-Champaign;University of Illinois at Urbana-Champaign;University of Illinois at Urbana-Champaign;University of Illinois at Urbana-Champaign

  • Venue:
  • Proceedings of the 19th annual international conference on Supercomputing
  • Year:
  • 2005

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Abstract

Chip Multiprocessors (CMPs) are flexible, high-frequency platforms on which to support Thread-Level Speculation (TLS). However, for TLS to deliver on its promise, CMPs must exploit multiple sources of speculative task-level parallelism, including any nesting levels of both subroutines and loop iterations. Unfortunately, these environments are hard to support in decentralized CMP hardware: since tasks are spawned out-of-order and unpredictably, maintaining key TLS basics such as task ordering and efficient resource allocation is challenging.While the concept of out-of-order spawning is not new, this paper is the first to propose a set of microarchitectural mechanisms that, altogether, fundamentally enable fast TLS with out-of-order spawn in a CMP. Moreover, we develop a fully-automated TLS compiler for aggressive out-of-order spawn. With our mechanisms, a TLS CMP with four 4-issue cores achieves an average speedup of 1.30 for full SPECint 2000 applications; the corresponding speedup for in-order only spawn is 1.04. Overall, our mechanisms unlock the potential of TLS for the toughest applications.