Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!apple!malcolm
From: malcolm@Apple.COM (Malcolm Slaney)
Newsgroups: comp.unix.cray,comp.sys.super
Subject: Re: Cray Autotasking
Message-ID: <36833@apple.Apple.COM>
Date: 29 Nov 89 00:32:50 GMT
References: <MCCALPIN.89Nov27080806@masig3.ocean.fsu.edu>
Distribution: usa
Organization: Apple Computer Inc, Cupertino, CA
Lines: 22

In article <MCCALPIN.89Nov27080806@masig3.ocean.fsu.edu> mccalpin@masig3.ocean.fsu.edu (John D. McCalpin) writes:
>Does anyone know offhand how the Cray autotasking splits loops between
>processors?  Specifically, in the following loop:
>	do 200 iseg=1,8
>	    do 100 i=istart(iseg),istop(iseg)
>		a(i,j(iseg)) = b(i,j(iseg))+two*c(i,j(iseg))
>   100	    continue
>   200	continue

You should sort them with the ones taking the longest time going first
in the loop.  For example, if you have one very large segment and lots of
little ones you don't want to do all the little ones first and then have
all the other processors waiting for the last (big) one to finish.  I think
I remember looking at the assembler generated and seeing that each processor 
just takes the next iteration in sequence.

I'm pretty sure that Autotasking and MicroTasking are identical in this 
regard.

Now, if I can just get my hands on a version of Standard C that autotasks....

								Malcolm