Cray Autotasking

[David E. Bernholdt]

In article <5414 at internal.Apple.COM> koeninger at apple.com (R. Kent Koeninger) writes:
>If autotasking is up-to-snuff, you would present it with one long loop, 
>and it would vectorize and parallelize that one loop for you, choosing a 
>fairly optimum distribution.
>
>Does anyone know if autotasking will split one loop into multiple tasks of 
>vectorized loops yet?  My assumptions is autotasking works like 
>microtasking.  Is this assumption valid?

I've messed around with autotasking a little.  It will do this.  In
fact, if you take a look at the source code after its been through the
compiler's preprocessors, you'll see that there are tests inserted on
the length of the vectors to decide how to distribute the work.

In other words, if the loop isn't long enough to warrent it, it won't
be parallelized, but if it is, it will "stripmine" the loop -- send
pieces out to be done in parallel on the available CPUs.  By giving
some command-line or (perhaps) source-embedded directives, oyu can
change the tolerances it uses to make these decisions.

I recommend the Cray Autotasking User's Guide (unfortunately I'm not at the
office, so I can't get the number for it) -- interesting reading.


-- 
David Bernholdt			bernhold at qtp.ufl.edu
Quantum Theory Project		bernhold at ufpine.bitnet
University of Florida
Gainesville, FL  32611		904/392 6365