Cray Autotasking
John D. McCalpin
mccalpin at masig3.ocean.fsu.edu
Tue Nov 28 00:08:06 AEST 1989
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
Does a 4-cpu system do iterations like this
cpu # iseg
----- ----
0 1,2
1 3,4
2 5,6
3 7,8
or like this
cpu # iseg
----- ----
0 1,5
1 2,6
2 3,7
3 4,8
I plan to sort the segments by length to help with load balancing, and
need to know which segments go to which cpu so that I can decide
exactly how to sort them.
--
John D. McCalpin - mccalpin at masig1.ocean.fsu.edu
mccalpin at scri1.scri.fsu.edu
mccalpin at delocn.udel.edu
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