[Beowulf] K Computer built for speed, not use

Vincent Diepeveen diep at xs4all.nl
Wed Oct 10 17:05:18 PDT 2012


I haven't seen many benchmarks of the Fujitsu SPARC64 VIIIfx that K  
computer is supposed to have,
yet from the outside it seems to me as a very capable CPU.  
Complaining one is allowed to do after having
a go at it trying to rewrite software for it.

It's simply not realistic in this many core age to suppose you can  
keep running your software without rewriting it
for new architecture, a box which had a cost of 1.4 billion dollar.  
If you want to take a look in the future with such
a 1.4 billion dollar box, then you have to write software that can  
use it.

On Oct 11, 2012, at 1:31 AM, Mark Hahn wrote:

>> http://www.sciencemag.org/content/338/6103/26.full?rss=1
> ...
>> Interesting claim. What kind of architecture structure would benefit
>> Linpack and would hinder real-world applications?
>
> my guess is they don't like vector.
>
> the quote appears to be from Jun Makino, the GRAPE guy
> (so qualifies as "sour grapes!).  there is a hint of critique
> in http://jun.artcompsci.org/talks/oookayama20120116.pdf
> (which if I read between the lines is saying that for his
> kind of astrophysics, he wants accelerator-type architectures,
> which differ significantly from vector archs in their relation
> of cpu and memory.  the "1+3 architectures" table seems to show
> a desire for dramatically lower B/F (bytes of memory BW per flop?)
> as well as much lower M/F.
>
> as for linpack being a bad benchmark, that's just bullshit.
> it's a benchmark.  it's not your application.  it does a good job
> of telling us about a form of performance that is well-understood.
> yes, you can make a very good guess at HPL performance if you know
> ncpus, peak FP rate and the interconnect performance - but conversely,
> a benchmark which is unpredictable is nothing to brag about!
>
> as for the criticism of K's process, well, making sausage is ugly.
> everything about a big project is sausage-like, and K is a fairly
> remarkable success given the range of issues it had to span.
> even ignoring the politics and finance, a sparc chip (!) that does
> very wide SIMD, with a memory system to support it, a cooling design
> to keep it going, and interconnect to scale.
>
> the only thing that pains me about the whole thing is that I don't  
> guess
> all the lessons learned will be propagated or leveraged.  mini-K will
> not be coming to a center near you.  there won't be an commodity chip
> that gets "now with added K sauce"...
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