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

[Michael Creel]

On 10/9/07, Jeffrey B. Layton <laytonjb at charter.net> wrote:
>
> 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
>
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I have done this with ParallelKnoppix, on a cluster of 2 2X Xeon 64 bit
machines. Running 4 MPI ranks on a 4 node completely virtualized 32 bit PK
cluster using VMware server is about 70-80% as efficient as a real 2 node PK
cluster running 4 MPI ranks. That's one data point, so worthless by itself
that I won't bother describing exactly what I did.
Michael
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