Optimistic active messages: a mechanism for scheduling communication with computation

  • Authors:

  • Deborah A. Wallach;Wilson C. Hsieh;Kirk L. Johnson;M. Frans Kaashoek;William E. Weihl

  • Affiliations:

  • M.I.T. Laboratory for Computer Science, Cambridge MA;M.I.T. Laboratory for Computer Science, Cambridge MA;M.I.T. Laboratory for Computer Science, Cambridge MA;M.I.T. Laboratory for Computer Science, Cambridge MA;M.I.T. Laboratory for Computer Science, Cambridge MA

  • Venue:
  • PPOPP '95 Proceedings of the fifth ACM SIGPLAN symposium on Principles and practice of parallel programming
  • Year:
  • 1995

Quantified Score

Hi-index 0.00

Visualization

Abstract

Low-overhead message passing is critical to the performance of many applications. Active Messages reduce the software overhead for message handling: messages are run as handlers instead of as threads, which avoids the overhead of thread management and the unnecessary data copying of other communication models. Scheduling the execution of Active Messages is typically done by disabling and enabling interrupts, or by polling the network. This primitive scheduling control, combined with the fact that handlers are not schedulable entities, puts severe restrictions on the code that can be run in a message handler. This paper describes a new software mechanism, Optimistic Active Messages (OAM), that eliminates these restrictions; OAMs allow arbitrary user code to execute in handlers, and also allow handlers to block. Despite this gain in expressiveness, OAMs perform as well as Active Messages.We used OAM as the base for an RPC system, Optimistic RPC (ORPC), for the Thinking Machines CM-5 multiprocessor; it consists of an optimized thread package and a stub compiler that hides communication details from the programmer. ORPC is 1.5 to 5 times faster than traditional RPC (TRPC) for small messages and performs as well as Active Messages (AM). Applications that primarily communicate using large data transfers or are fairly coarse-grained perform equally well, independent of whether AMs, ORPCs, or TRPCs are used. For applications that send many short messages, however, the ORPC and AM implementations are up to three times faster than the TRPC implementations. Using ORPC, programmers obtain the benefits of well-proven programming abstractions such as threads, mutexes, and condition variables, do not have to be concerned with communication details, and yet obtain nearly the performance of hand-coded Active Message programs.