Off topic - G5 question

graham.mullier at syngenta.com graham.mullier at syngenta.com
Fri Jun 27 05:28:55 EDT 2003


I think Rob made an excellent point. I'd like to paraphrase: optimising for
a very unusual architecture, with poor support from the compilation (etc)
tools, should not be undertaken lightly.

I've seen examples in my time of very promising (=hyped) add-on hardware
units for Vaxes, IBM mainframes, plus complex specialised graphics systems
(E&S PS390) that either didn't live up to the promised performance, or where
the effort involved to make use of the specialised hardware made it
difficult to justify the work.

Vax - the extra units seemed to offer performance similar to the strange new
(to me at the time) Unix machines. So we bought an SGI server and once we'd
got over the shock found it very useful because it was so flexible, with
good compilation tools.

IBM - we never saw the supposed performance improvement, and the only way to
get calculations (large ab initio molecular orbital calculations) onto the
system was to hand-deliver a tape (1/4-inch reel...). We suggested that the
vector unit wasn't worth it for our work.

E&S PS390 - goodwhen someone else wrote the graphics code, nightmare when it
was someone in our group. He produced an excellent general visualisation
system for 3D scatter plots but when we stopped using the hardware we had to
throw away the code. Not a good use of resources.

I prefer good general-purpose systems where other people help me by working
on the tools necessary to make best use of the hardware.

Graham


Graham Mullier
Chemoinformatics Team Leader,
Chemistry Design Group,
Syngenta, Bracknell, RG42 6EY, UK.
direct line: +44 (0) 1344 414163
mailto:Graham.Mullier at syngenta.com



-----Original Message-----
From: Robert G. Brown [mailto:rgb at phy.duke.edu]
Sent: 26 June 2003 23:12
To: Mark Hahn
Cc: Beowulf Mailing List
Subject: Re: Off topic - G5 question


[...]

Oh, that's ok.  I freely admit to utter irresponsibility.  Laziness too!

I was (of course) at least partly tongue in cheek, although the nugget
of truth in what I was saying is what I'd call the "CM5 phenomenon".
[...]
This kind of architecture makes me very nervous.  Optimizing is no
longer just a matter of picking good compiler flags or writing core
loops sensibly (things that can easily be changed or that are good ideas
on nearly any architecture); [...]

It is this lack of portability that can, and I say can, be a killer to
productivity and ultimately to one's ability to select freely from COTS
architectures.  Once the code is modified and optimized for (say) a G5,
one has to take into account the ADDITIONAL cost of un/remodifying it
and reoptimizing it for (say) an Opteron or Itanium or
whateverisnextium.  [...]
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