I am comparing a linear algebra algorithm written in Fortran with my own
Chapel implementation of the same algorithm. About 90% of the computation
time of (slightly more than) half of my algorithm is an operation which
can be written as
inline proc tpxyT(ref t : [?tD] ?R, const ref x : [] R, const ref y : [] R)
{
const (rows, columns) = tD.dims();
[ (i, j) in tD ] t[i, j] += x[i] * y[j];
}
I will come back to the above shortly.
I want to compare my code against Fortran.
I want this comparison to be beyond fair! That is the bottom line on this
posting but do feel free to tell me the above code is less than perfect.
Looking at the last line, it is highly parallelizable. But, I assume when
called from somewhere within a routine that is itself called from with a
serial block, and with the program also fed
--dataParTasksPerLocale=1
then no parallelization will happen, i.e. that construct is just a
whopping great hint to the optimizer.
Is my guess correct?
Would people agree that using this Chapel feature is still scrupulously
fair (in my comparison against Fortran)?
If Chapel vectorized remotely well, the following is superior:
[i in rows] t[i, ..] += x[i] * y;
But Chapel is not so good on vectorization, so this approach was dropped.
Note that compared to the first approach and with matrices of the size of
1600*1600 to 4000*4000, my semi-rigorous experiments suggest that this has
somewhere between 10-20% longer run-time using 1.22.0 and a GCC backend
and various Intel Xeon CPUs. I think this second line is a far superior
description of what I am trying to do and I await better vectorization
in Chapel. I was thinking of writing some C-code to do
t[i,..] += x[i] * y
but then realised that I have not a clue how to write an interface like
proc tupv(n : int, m : int, t : T, ref u : [] T, const ref v [] T)
where T is real(32) or real(64) and then use that interface or even if
that interface would be the best one.
Thanks - Damian
Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
Views & opinions here are mine and not those of any past or present employer
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