\begin{abstract}
In all-to-all personalized communication (AAPC), every node of a
parallel system sends a potentially unique packet to every other node.
AAPC is an important primitive operation for modern parallel
compilers, since it is used to redistribute data structures
during parallel computations. As an extremely dense communication
pattern, AAPC causes congestion in many types of networks
and therefore executes very poorly on general purpose, asynchronous
message passing routers.

We present and evaluate a network architecture that executes
all-to-all communication optimally on a two-dimensional torus.  The
router combines optimal partitions of the AAPC step with a self-synchronizing switching mechanism integrated into a conventional
wormhole router. Optimality is achieved by routing along shortest
paths while fully utilizing all links.  A simple hardware addition for
synchronized message switching can guarantee optimal AAPC routing in
many existing network architectures.

The flexible communication agent of the iWarp VLSI component allowed
us to implement an efficient prototype for the evaluation of the
hardware complexity as well as possible software overheads.  The
measured performance on an $8 \times 8$ torus exceeded 2 GigaBytes/sec
or 80\% of the limit set by the raw speed of the interconnects.  We
make a quantitative comparison between the AAPC router and a
conventional message passing system on the same machine, and we
compare these methods with optimized AAPC performance published for
other parallel machines. The potential gain of such a router for
larger parallel programs is illustrated with the example of a
two-dimensional Fast Fourier Transform.
\end{abstract}
























 
