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6.1.2.2 MPP systems
MOLPRO will in principle
run on distributed-memory multiprocessor systems,
including workstation clusters, under
the control of the
Global Arrays
parallel toolkit. In practice, many parts of the code are not
parallelized in this way, and therefore run with replicated
work. Additionally, some of those parts which have been parallelized
rely on fast inter-node communications, and can be very inefficient
across ordinary networks. Therefore, at present, some caution is
needed to avoid waste of resources in a multiuser environment.
A programming model has been adopted in which disk I/O is simulated within
the global memory of all processors. This avoids potential bottlenecks
arising from many processors simultaneously trying to do I/O, taking
advantage of the large total memory in a typical MPP machine in order to
store all two-electron integrals and other quantities in memory.
By default, all unnamed MOLPRO files
are implemented in this way. The amount of memory available for such
activities is reserved in advance, and can be adjusted by setting the
environment variable MOLPRO_GA_MEMORY
, which specifies a number of
8-byte words to be used on each processor. This memory is distinct from,
and not available to, the normal workspace specified in the
memory input command.
Next: 6.1.2.3 Specifying parallel execution
Up: 6.1.2 Running MOLPRO on
Previous: 6.1.2.1 SMP systems
P.J. Knowles and H.-J. Werner
molpro-support@tc.bham.ac.uk
Mar 8, 2000