Re: Linux, the microkernel (was Re: latest linus-2.5 BK broken)

[Jakob Oestergaard]

On Sun, Jun 23, 2002 at 11:15:53AM -0400, Sandy Harris wrote:
> Larry McVoy wrote:
> 
...
> Also, it isn't as clear that clustering experience applies. Are clusters
> that size built hierachically? Is a 1024-CPU Beowulf practical, and if so
> do you build it as a Beowulf of 32 32-CPU Beowulfs? Is something analogous
> required in the OSlet approach? would it work?

Well yes and no.  Often the hierarchy is really shallow. A typical
(larger) Beowulf (if such a thing exists) could be ~50 nodes per 100Mbit
switch, heaps of those switches go into (interconnected) gigabit
switches, and that's it.  There are *many* 'wulfs out there with just
one or a few switches - but they are not 1024 CPUs either.

Much more specialized interconnects are often used. The SP/2 (IBM) used
something resembling "one big switch", which was in reality a number of
cleverly connected smaller switches (sorry, forgot the topology) - so no
real hierarchy, similar bandwidth and latency between any two nodes an a
several-hundred node cluster.

The "Earth Simulator" (the #1 on www.top500.org) is using a one-stage
crossbar for it's 5000+ nodes.

My personal pet theory is, in short, that the hardware stays fairly flat
- not because it is beneficial to (on the contrary!), but because
software assumes that it is flat.  The software paradigms in practical
use today have not changed since the early '80s and as long as the
hardware manages to stay "almost flat" that's not going to change.

-- 
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