[Beowulf] Virtualisation and high performance interconnects.

[Mark Hahn]

> However, it does for all non-OS-bypass operations. The most important of 
> these is memory registration, because it's not a one-time cost as the Ohio 
> State papers have always portrayed it. For applications that do not

it's also worth pointing out that virtualization introduces some 
amount of jitter to a parallel application's timing.  this will not
matter at all if the app is fairly small and/or loosely-coupled.
but for nontrivial sized jobs that message frequently or in large
collectives...