[Beowulf] vectors vs. loops

Vincent Diepeveen diep at xs4all.nl
Wed Apr 27 07:08:34 EDT 2005


Way easier is a few libraries that do the entire matrix or invariant
calculation for you.

What i am always amazed about is that todays supercomputers cost tens of
millions and maintenance even more (as there is sysadmin staffs of tens of
people and i had to work with many organisations for example with all paid
dudes who just add to burocracy, this in order to run at an outdated
supercomputer with 500Mhz processors, still equipped with OFF chip L2 cache
!!!, whereas my competitors ran on 2.8Ghz Xeon MP's).

Yet the majority of code running at it, is so so childish written.

This where i've been programming for many years to have my code run
parallel very well. It also runs on pc's and must perform real well too
when running single cpu, competing with tens of other programs.

Government could easily afford paying a few persons making code running
ideal on those machines.

There is several real good programmers.

What i've seen running there, it would not be nice to start describing it
here, but some really have no clue about programming.

They program something in 1980, and the next 30 years it is running and
eating system time. That system time, because of the burocracy, is
practical very expensive, so a coder speeding them up bigtime would be a
big help.

A good coder can let the majority of the software run faster on a PC, than
it runs on those supercomputers.

I met one programmer who a year or 10 ago helped a german project speed up;
 he managed to speedup a certain program a factor 1 million for his
department, by adding fast fourier transforms to the code. 

1 coder saving out tens of millions of dmarks.

At 10:10 PM 4/26/2005 -0400, Andrew Piskorski wrote:
>On Tue, Apr 26, 2005 at 10:01:25AM -0500, Ben Mayer wrote:
>
>> I actually just did a small study of how well students in a parallel
>> computing class write parallel codes on X1 with MPI and UPC. One of
>> the things that stood out is that they tended to do odd things in
>> their loops that inhibit code from vectorizing.
>
>So, why were these students writing loops in the first place?  If the
>goal is to generate vectorized code, wouldn't it make more sense to
>use a language or library which directly supports vector commands?
>
>E.g., although they're used for serial not parallel programming, S and
>R are vector oriented in a pleasantly convenient way.  There do exist
>languages and libraries specifically intended for vector programming,
>like CVL or NESL, right, so, are they not useful?
>
>
http://www-2.cs.cmu.edu/afs/cs.cmu.edu/project/scandal/public/papers/cvl.html
>  http://www-2.cs.cmu.edu/~scandal/
>
>-- 
>Andrew Piskorski <atp at piskorski.com>
>http://www.piskorski.com/
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