BIB-VERSION:: CS-TR-v2.0
          ID:: STAN//CSL-TR-92-546
       ENTRY:: November 02, 1994
ORGANIZATION:: Stanford University, Computer Systems Laboratory
       TITLE:: THE ACCURACY OF TRACE-DRIVEN SIMULATIONS OF MULTIPROCESSORS
        TYPE:: Technical Report
      AUTHOR:: Goldschmidt, Stephen R.
      AUTHOR:: Hennessy, John L.
        DATE:: September 1992
       PAGES:: 47
    ABSTRACT:: In trace-driven simulation, traces generated for one set of
               machine characteristics are used to simulate a machine with
               different characteristics. However, the execution path of a
               multiprocessor workload may depend on the ordering of events
               on different processors, which in turn depends on machine
               characteristics such as memory system timings. Trace-driven
               simulations of multiprocessor workloads are inaccurate unless
               the timing-dependencies are eliminated from the traces. We
               measure such inaccuracies by comparing trace-driven
               simulations to direct simulations of the same workloads. The
               results were identical only for workloads whose timing
               dependencies were eliminated from the traces. The remaining
               workloads used either first-come first-served scheduling or
               non-deterministic algorithms; these characteristics resulted
               in timing-dependencies that could not be eliminated from the
               traces. Workloads which used task-queue scheduling had
               particularly large discrepancies because task-queue
               operations, unlike other synchronization operations, were not
               abstracted. Two types of simulation results had especially
               large discrepancies: those related to synchronization latency
               and those derived from relatively small numbers of events.
               Studies that rely on such results should use timing-
               independent traces or direct simulation.
       NOTES:: [Adminitrivia V1/Prg/19941102]
         END:: STAN//CSL-TR-92-546