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Isotach Prototype |
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Goals
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Design and build a prototype isotach system that implements isotach logical
time at a low cost, in a scalable way, using primarily commodity parts
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Show that isotach systems reduce synchronization overhead in distributed
computations
Description of the Prototype
The prototype isotach system consists of a commodity network (Myrinet)
and processors (PCs running Linux) in
combination with two types of isotach-specific devices:
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switch interface units (SIUs) — one per host
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token managers (TMs) — one per switch
The SIUs and TMs will plug into the Myrinet network through Myricom's soon
to be forthcoming FI chips.
The SIUs are in-link between the host and neighboring switch, i.e.,
they appear to be a thick part of the wire between the host and switch.
Ideally the SIU is located on the same chip as the processor. A second
choice would be to attach the SIU to the memory bus. Each TM occupies one
port of a Myricom switch. Ideally the TM logic will be integrated
into the switch itself.
The resulting technology will impose little or no burden on non-isotach
traffic. Non-isotach traffic takes a fast route around the SIU for the
source and destination hosts. Hosts not running isotach apps do not need
an SIU. Switches through which no isotach traffic passes do not need
TMs. The project is nearing completion of the design for the
TMs and SIUs.
V1 Prototype
An initial (V1) prototype in which the functionality of the TMs and SIUs
is emulated in software running on the PCs and network interface units.
Performance studies of the V1 prototype indicate that even with software
emulation of isotach components, the cost of maintaining isotach logical
time is low --- approximately a doubling of message latencies over an Illinois
Fast Messages implementation on the same hardware. Simulation studies
comparing isotach and non-isotach systems show order of magnitude improvements
for isotach system under the assumption that the latency of an isotach
message is double that of a non-isotach message, Thus we expect that the
isotach prototype will provide a good performance
trade-off: greatly enhancing the ability of processes to take advantage
of a system's raw power, without greatly reducing that power.
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