Introduction

ROSS is an acronym for Rensselaer's Optimistic Simulation System. It is a
parallel discrete-event simulator that executes on shared-memory
multiprocessor systems. ROSS is geared for running large-scale simulation
models (i.e., 100K to even 1 million object models).  The synchronization
mechanism is based on Time Warp. Time Warp is an optimistic
synchronization mechanism develop by Jefferson and Sowizral [10, 11] used
in the parallelization of discrete-event simulation. The distributed
simulator consists of a collection of logical processes or LPs, each
modeling a distinct component of the system being modeled, e.g., a server
in a queuing network. LPs communicate by exchanging timestamped event
messages, e.g., denoting the arrival of a new job at that server.

The Time Warp mechanism uses a detection-and-recovery protocol to
synchronize the computation. Any time an LP determines that it has
processed events out of timestamp order, it "rolls back" those events, and
re-executes them. For a detailed discussion of Time Warp as well as other
parallel simulation protocols we refer the reader to [8]

ROSS was modeled after a Time Warp simulator called GTW or Georgia Tech
Time Warp[7]. ROSS helped to demonstrate that Time Warp simulators can be
run efficiently both in terms of speed and memory usage relative to a
high-performance sequential simulator.

To achieve high parallel performance, ROSS uses a technique call Reverse
Computation. Here, the roll back mechanism in the optimistic simulator is
realized not by classic state-saving, but by literally allowing to the
greatest possible extent events to be reverse. Thus, as models are
developed for parallel execution, both the forward and reverse execution
code must be written. Currently, both are done by hand. We are
investigating automatic methods that are able to generate the reverse
execution code using only the forward execution code as input. For more
information on ROSS and Reverse Computation we refer the interested reader
to [4, 5]. Both of these text are provided as additional reading in the
ROSS distribution.

License

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