VM and performance (was Re: [Beowulf] best Linux distribution)

[Jeffrey B. Layton]

The recent emails from rgb and Doug lead me to a question. Has anyone
tested codes running under a VM versus running them "natively" on
the hardware (native isn't a good word and I hope everyone gets my
meaning)?  The last word I heard is that performance takes a substantial
hit if you are running a code in a VM. Some of the reasons are that the
code has only virtualized access to the hardware (particularly the NICs)
and memory management is a bit more difficult (although Barcelona with
nested page tables should help there). I do remember VirtualIron saying
that they had IB drivers so that the VM had direct access to the hardware.

Thanks!

Jeff