Unisys

[Simen Timian Thoresen]

> On Mon, 26 Feb 2001 kragen at pobox.com wrote:
> 
> > FWIW, big SMPs will tend to do shared-memory things more efficiently
> 
> Shared memory is unphysical. Don't use it for code with expected long
> lifetime. You're facing relativistic lag problems, signal fanout problems
> (multiport memory is expensive to do), and the nightmare of cache
> coherency. Most of it is hidden in current overhead/inefficiencies,
> but it's there.
> 
> > than machines that actually have to pass messages to simulate shared
> > memory, and some people think writing a threaded program that scales
> 
> If you want to access bits stored in a remote piece of hardware (such as a
> memory chip), you apply a bit pattern, selecting a group of bits, and
> recieve said bit pattern. If this is not message passing, I don't know
> what message passing is.
> 
> It is handled in hardware, but there is no reason why distributed memory
> could not be emulated by hardware on an efficient message-passing
> infrastructure.
> 
While this does not apply directly to this, this is exactly what the Dolphin 
ICS SCI hardware does. It is a shared memory interconnect offering remote 
memory reads and writes and remote to local memory mappings.

As to simulating shared memory with messages - Scali has developed a 
high-speed MPI on top of this, so that then is simulating message passing 
on shared memory.

Yours,
-Simen Thoresen, Dolphin ICS systems administrator
--
Why are there penguins embedded in my toaster?

Er det rart?
The gnu RART-project on http://valinor.dolphinics.no:1080/~simentt/rart