Jeffrey B. Layton 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
You have two major types, the heavyweight emulators (VMware, et al) and
the lighter weight hypervisors. I have seen studies of various codes
that show not a huge hit ... the caveat being that these codes spent
very little time in system calls (usually thunked to the host somehow)
and most of the time computing.
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.
The more layers you have to pass through, the lower your overall
performance (of course).
Thanks!
Jeff
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