Re: [9fans] "FAWN: Fast array of wimpy nodes" (was: Plan 9 - the next 20 years)

[tlaronde@polynum.com]

On Sun, Apr 19, 2009 at 09:27:43AM -0500, Eric Van Hensbergen wrote:
>
> I'm not convinced that such ad-hoc DSM models are the way to go as a
> general principal.  Full blown DSM didn't fair very well in the past.
> Plan 9 distributed applications take a different approach and instead
> of sharing memory they share services in much more of a message
> passing model.  This isn't to say that all caches are bad -- I just
> don't believe in making them the foundation of your programing model
> as it will surely lead to trouble.
>

FWIW, the more satisfying definition for me of a "computing unit" (an
"atom" OS based) is memory based: all the processing unit having direct
hardware access to a memory space/sharing the same directly hardware
accessible memory space.

There seems to be 2 kinds of "NUMA" around there :

1) Cathedral model NUMA: a hierarchical association of memories, tightly
coupled but with different speeds (a lot of uniprocessor are NUMA these
days with cache1, cache2 and main memory). All directly known by the
cores.

2) Bazaar model NUMA, or software NUMA, or GPLNUMA: treating an
inorganized collection of storage as addressable memories since one can
always give a way to locate the ressource, including by URL, associating
high speed tightly connected memories with remote storage accessible via
IP packets sent by surface mail if the hardware drived whistle is heard
by the human writing the letters.

Curiously enough, I believe in 1. I don't believe in 2.
--
Thierry Laronde (Alceste) <tlaronde +AT+ polynum +dot+ com>
                 http://www.kergis.com/
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