[Beowulf] Linux quality vs. defects
landman at scalableinformatics.com
Mon May 13 10:41:17 PDT 2013
On 05/13/2013 01:21 PM, Peter St. John wrote:
> Well that was facile of me. I was thinking universities didn't teach
> fortran anymore, but I see that the UNC research computing support group
> currently supports three brands (gnu, intel, and portland) for each of
> all three of fortran, C, and C++ compilers.
Yeah ... pretty much every time a CS person incredulously wonders why
anyone would *evuh* use such a horrible old language (Fortran of
course), lots of physical scientists, chemists, astronomers, and others
say something to the effect of "you can have my language when you pry it
from my cold dead fingers."
The Fortran of today doesn't look much like F77, or F66. Quite a modern
little language there. And it optimizes very well. Just doesn't know
much about parallelism ... no wait, f2008 does.
Fortran was described first in a paper in 1957 by Backus and team. This
is a 56 year old language, and its still going strong. Rumors of its
demise are something of an exaggeration. Whats more amusing than these
rumors, are the myriad of (fad) languages proposed to take over its
I have to admit that my mad 4tran skillz are atrophying due to lack of
use. Mostly a Perl, C, and (oh my gosh) Node coder these days. Every
once in a while I'll pull out some of my old (20+ year old) code to play
with it. The Fortran and Perl work. C ... its a toss up, and the C++?
Fuggedaboutit. I won't even think to try the Pascal, Modula2, and
other bits I played with (anyone remember Prolog or APL?).
To circle back to beowulfery ... I think that what matters most is
finding something you can be productive with, and run in parallel on a
distributed memory/shared nothing architecture. This is what Beowulfery
enables (though with vSMP you can have the best of both worlds). Having
a language that enables you to naturally express your problem, and that
knows how to map correctly onto the underlying architecture ... that
would be wonderful. That is the hard problem implicit in this. Fast
serial code often doesn't make terribly good parallel code, and
sometimes poor serial code winds up showing excellent parallel
capability, though you often have to graft the parallelism onto the code
... so its not quite serial anymore.
And that is, in beowulfery, where many code defects I see come from.
Getting parallelism right is non-trivial at best. Compilers cannot be
made infinitely smart, they don't do a great job of hyperoptimizing to
the parallel/serial architectures. They have to make engineering
tradeoffs between faster and more correct/accurate. Some times
combining these tradeoffs with elements of the code design can lead to
... erm ... spectacular failures.
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: landman at scalableinformatics.com
web : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
More information about the Beowulf