>
> BTW, para-virt is faster.
>
Mostly true but not completely. para-virt is faster overall but full
virt is *supposed* to be faster for CPU processing. I put stars around
supposed because I've never gotten full virt to work and so I haven't
done my own testing. I've had to go on what other people say.
When I did my testing of paravirtualization prior to the IU LinuxFest
presentation I did, I found that Xen domUs where about 5% slower than
the native CPU speed. Which honestly is pretty fast compared to other
emulators and things like VMWare. I did this test by creating a special
VM that all it did was render the standard benchmarking frame in POVRay
(3d raytracer) and compare it with how long it took in a native non-Xen
kernel. Then I'd copy this VM and run X amount of them at the same time
to test the results with Xen. This was done on a single Pentium 4
2.4GHz with 2GB of RAM. Each VM only needed something like 96MB so I was
able to run around 16 at once.
Interestingly, the CPU was most efficient when I ran 8 VMs at once. If
I ran 4, 6, 10 or 12 it was less efficient. This is in terms of work done in
the same amount of time.
I've used this 8 VM results as the policy at Suso for how many VMs we
allow per core on our Xen service. 8 per core seems to be a good
balance between getting good usage out of the CPU and not making
everybodys VM seem slow. Then of course multiple cores help when there
are deviations from the norm.
I've been pretty impressed with the VMs responsiveness even under
significant load on the host machine or other VMs. They did a good job
with the scheduler.
One thing interesting is that the consultant from RH that was at Cook
last month, went to go work for Dreamworks Animation after he helped us
and he said he was going to setup a renderfarm for them that utilized
Xen. That struck me as interesting since I would think that you'd want
all the raw processing power you could get for rendering and what is the
use of segregating it. Oh well, I don't know anything other than that
about their setup.
--
Mark Krenz
Bloomington Linux Users Group
http://www.bloomingtonlinux.org/
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