Software Distributed Shared Memory Systems

In collaboration with researchers from Rice, I have conducted research on using software DSM to link networks of shared memory multiprocessors seamlessly, providing bigger shared memory systems. We were one of the first to show the viability of this approach. With SMP clusters and fast interconnects becoming increasingly available, this research is highly relevant today. This work was presented at the 1994 ISCA conference.

In more recent work, I have compared two relaxed memory models used in software DSM systems. Lazy release consistency (LRC) makes the entire address space consistent at synchronization points. In contrast, entry consistency (EC) uses programmer annotations to make portions of the shared address space consistent at synchronization points. EC requires these annotations for correctness. For each model, we implemented several systems to address the different design choices. The extra programming effort under EC is expected to improve performance. However, our research offers compelling empirical evidence to the contrary; the programmer annotations required by EC did not consistently improve performance over LRC. In fact, for some applications, the LRC implementations outperformed the EC ones. I presented this work at the 1996 HPCA conference.

Relevant Publications:

• Software vs. Hardware Shared Memory Implementation: A Case Study,
  with Alan Cox, Sandhya Dwarkadas, Peter Keleher, Honghui Lu and Willy Zwaenepoel
  Proceedings of the 21st International Symposium on Computer Architecture, April 1994.

• TreadMarks: Shared Memory Computing on Networks of Workstations,
  with Cristiana Amza, Alan Cox, Sandhya Dwarkadas, Peter Keleher, Honghui Lu, Weimin Yu, and Willy Zwaenepoel, IEEE Computer, February 1996.

• A Comparison of Entry Consistency and Lazy Release Consistency Implementations
  with Sarita Adve, Alan Cox, Sandhya Dwarkadas and Willy Zwaenepoel,
  Proceedings of the 2nd International Symposium on High-Performance Computer Architecture, February 1996.

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