[Beowulf] Rackable / SGI

Greg Lindahl lindahl at pbm.com
Sat Apr 4 15:19:02 EDT 2009


On Sat, Apr 04, 2009 at 04:06:22PM +0200, Eugen Leitl wrote:
> On Fri, Apr 03, 2009 at 01:32:13PM -0700, Greg Lindahl wrote:
> 
> > > Will have to do with embedded memory or stacked 3d memory a la
> > > http://www.cc.gatech.edu/~loh/Papers/isca2008-3Ddram.pdf
> > 
> > We've been building bigger and bigger SMPs for a long time, making
> > changes to improve the memory system as needed. How is multicore any
> 
> Off-die memory bandwidth and latency are limited, so many codes
> start running into memory bottlenecks even at moderate number
> of cores

Exactly like shared-bus multiprocessors.

The incremental method of solving this is what Opteron/Nehalem does.
The more radical method is what Origin/Altix did. It all comes down to
how many pins you're willing to commit to memory and how few pins you
can squeeze a memory bus down to; once you bump up against that limit,
then you need an improvement in packaging, which is no more radical
than what Opteron/Nehalem or Origin/Altix did. And, of course, all
this was invented before Opteron or Origin.

The sky is not falling.

-- greg

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