-------------- Original message --------------
From: "Toon Knapen" <[EMAIL PROTECTED]>
How come there is almost unanimous agreement in the beowulf-community while the
rest is almost unanimous convinced of the opposite ? Are we just tapping
ourselves on the back or is MP not sufficiently dissiminated or ... ?
Mmm ... I think the answer to this is that the rest of world (non-HPC world) is
in a time
warp. HPC went through its SMP-threads phase in the early-mid 1990s with
OpenMP, and then we needed more a more scalable approach (MPI). Now that
multi-core and multi-socket has brought parallelism to the rest of the
Universe, SMP-based parallelism has had a resurgence ... this has also
naturally caused some in HPC to revisit the question as nodes have fattened.
The allure of a programming model that is intuitive, expressive, symbolically
light-weight,
and provides a way to manage the latency variance across memory partitions is
irresistable.
I kind of like the CAF extension to Fortran and the concept of co-arrays. The
co-array is
and array of identical normal arrays, but one per active image/process. They
are defined as such:
real, dimension (N) [*] :: X, Y
If the program is run on 8 cores/processors/images the * becomes 8. 8, 1D
arrays of size
N are created on each processor. In any references to the locale component of
the co-array
(the image on the processor referencing it), you can drop the []s ... all other
references (remote)
must include it. This is symbolically light, but reminds the programmer of
every costly non-
local reference with the presence of the []s in the assignment or operation.
There is much
more to it than that of course, but as the performance gap between carefully
constructed
MPI applications and CAF compiled code shrinks I can see the later gaining some
traction
for purely programming elegance related reasons. If you accept that notion
that most MPI
programs are written at a B- level in terms of efficiency then the idea of gap
closing may not
be so far fetched. CAF is supposed to be include in the Fortran 2008 standard.
rbw
--
"Making predictions is hard, especially about the future."
Niels Bohr
--
Richard Walsh
Thrashing River Consulting--
5605 Alameda St.
Shoreview, MN 55126 --- Begin Message ---
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