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<H2><A NAME="SECTION04541000000000000000">Choosing a Faster BLACS Library</A></H2>
<P>
Users should choose
vendor-supplied BLACS optimized for their
computer;
these BLAS will
be the fastest BLACS implementation.
If no vendor-supplied BLACS exists, users will have to choose among
the publicly available BLACS libraries.
<P>
Many distributed-memory computers offer several
communication libraries. The SP2, for example,
offers MPI, PVM and MPL communication libraries.
Since implementations of the BLACS exist on
each of several communication libraries, one
may have a choice of several different BLACS
implementations. On the SP2, for example, the user can run the
BLACS MPI, BLACS MPL, or BLACS PVM version.
<P>
Unfortunately, no hard rule exists as to which
BLACS implementation will be fastest. However,
since the BLACS cannot be faster than the communication
library upon which it is built, and since the BLACS
typically add little overhead, it is usually best
to choose the BLACS implementation that is
based on the fastest communication library.
<P>
Identifying the fastest communication library may not
be trivial. The speed of communication libraries
may be reported in different ways. Moreover,
although the speed of blocking sends is reported because they are
faster than nonblocking sends, the BLACS must
use the nonblocking sends or provide its
own buffering. Those who are using one of the computers
listed in this chapter should refer to Tables <A HREF="node113.html#tabnode">5.2</A>
and <A HREF="node113.html#tabnode2">5.3</A>
to see which library we used for timing.
Our experience is that
the fastest communication
library was the library that is native to that
particular computer.
<P>
<BR> <HR>
<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
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