Re: [Qemu-devel] QEMU redesigned for MPI (Message Passing Interface)

[Paul Brook <paul@codesourcery.com>]

> > The practical example below will explain it completely:
> >
> > 1) we take 4 common modern computers - CoreQuad + 8 GB Memory.
> > 2) we assemble a standard Linux cluster with 16 cores and 32G memory.
> > 3) and now - we run the only one virtual guest system, but give it ALL
> > available resources.

If the guest isn't aware of this discontinuity then performance will really 
suck. Generally speaking you have to split jobs anyway, the same as you would 
on a regular cluster, the SSI just makes migration and programming a little 
easier.

If you don't believe me then talk to anyone who's used large SSI systems (e.g. 
SGI Altix) - these systems have dedicated hardware assist and interconnect 
designed for SSI operation and you still have to be fairly selective about how 
you use them.

> What you're describing is commonly referred to as a Single System
> Image.  It's been around for a while and can be found in software-only
> verses (pre-Xen VirtualIron, ScaleMP) and hardware-assisted (IBM, 3leaf).

Or better still do it at the OS level (e.g. OpenSSI).

Paul