On Oct 9, 2007, at 9:51 AM, Joe Landman wrote:
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.
Yup. My experience (although a little dated) was looking a codes
running under Xen (see previous post by RGB regarding the COD project
here at Duke). Computationally wise, there can be very low impact if
the system is set up right. With earlier versions of Xen, there was
significant overhead in the networking layer which could impact MPI
and other distributed codes that utilize the IP stack. This was
supposedly vastly improved in later versions of Xen, but I don't have
any data at hand.
I'm not sure how the user-space communication fabrics (OpenIB, etc.)
would fair under a VM environment, but theoretically they could be
quite good. It could make the VM overhead much more palatable in an
HPC environment.
-bill
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