[Beowulf] K Computer built for speed, not use

Mark Hahn hahn at McMaster.CA
Wed Oct 10 16:31:18 PDT 2012


> 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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