Tradeoffs in buffering speculative memory state for thread-level speculation in multiprocessors

  • Authors:

  • María Jesús Garzarán;Milos Prvulovic;José María Llabería;Víctor Viñals;Lawrence Rauchwerger;Josep Torrellas

  • Affiliations:

  • University of Illinois at Urbana-Champaign, Urbana, IL;Georgia Institute of Technology;Universitat Politècnica de Catalunya, Spain;Universidad de Zaragoza, Spain;Texas A&M University;University of Illinois at Urbana-Champaign, Urbana, IL

  • Venue:
  • ACM Transactions on Architecture and Code Optimization (TACO)
  • Year:
  • 2005

Quantified Score

Hi-index 0.00

Visualization

Abstract

Thread-Level Speculation (TLS) provides architectural support to aggressively run hard-to-analyze code in parallel. As speculative tasks run concurrently, they generate unsafe or speculative memory state that needs to be separately buffered and managed in the presence of distributed caches and buffers. Such a state may contain multiple versions of the same variable. In this paper, we introduce a novel taxonomy of approaches to buffer and manage multiversion speculative memory state in multiprocessors. We also present a detailed complexity-benefit tradeoff analysis of the different approaches. Finally, we use numerical applications to evaluate the performance of the approaches under a single architectural framework. Our key insights are that support for buffering the state of multiple speculative tasks and versions per processor is more complexity-effective than support for lazily merging the state of tasks with main memory. Moreover, both supports can be gainfully combined and, in large machines, their effect is nearly fully additive. Finally, the more complex support for storing future state in the main memory can boost performance when buffers are under pressure, but hurts performance when squashes are frequent.