VM and performance (was Re: [Beowulf] best Linux distribution)
andrew at moonet.co.uk
Tue Oct 9 10:48:03 EDT 2007
Seems to be some excitement in Europe over Xen, a paravirtualisation package.
On 09/10/2007, Joe Landman <landman at scalableinformatics.com> 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.
> > 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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> Joseph Landman, Ph.D
> Founder and CEO
> Scalable Informatics LLC,
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