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Re: [Xen-users] Measure disk activity in full-virtualization.

From: "Alain Barthe" <ab266061@xxxxxxxxx>

Date: Thu, 24 Jul 2008 12:45:03 +0200

Cc: Alejandro Paredes <aleparedes@xxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx

Delivery-date: Thu, 24 Jul 2008 03:45:52 -0700

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List-id: Xen user discussion <xen-users.lists.xensource.com>

2008/7/23 Todd Deshane <deshantm@xxxxxxxxx>:

>
> Sure, but concerning CPU isolation, I can't understand, theorically, that
> full virtualisation is better than para virtualisation. And our experiment
> confirms this. Can you explain this point ?

My understanding is that a lot of the CPU isolation comes from the scheduler.
The schedulers in modern operating systems in general should be good enough
to provide good isolation, regardless of para vs. full virtualization.

I agree. I suppose that the hypervisor scheduler does the job in PV, and the OS process scheduler does the job in FV. I am not sure they have the same policy, nor the same goals. Also, the hypervisor scheduler seems to be more tunable than the OS one.

Performance isolation is different than simple measuring overall performance and
I don't think that it is fundamental that full or para will be better
in general. The
implementation done by the scheduling mechanism both in the guest and of the
hypervisor matters. It is very possible that our CPU test was not
stressful enough.
It is also possible that the tests that you are doing stress more than
just the CPU
and the degradation noticed in the other guests is due some other factor such as
disk or network or even memory.

Yes. The test we done was roughly 5 parallel gzipped tar on big files, so I think that mainly the CPU and disk I/O were stressed. So you are right, we cannot compare your methodic benchmark with our simple and subjective experiment.

Our work is actually ongoing and choosing the right CPU-intensive test
will be an
important decision going forward.

Thanks for your questions/comments. Feel free to give suggestions etc.

I like to see that there is others doing performance isolation testing
now. When we
started, we didn't know of others doing that kind of testing.

Cheers,
Todd

Thanks for your reply.

--
Todd Deshane
http://todddeshane.net
check out our book: http://runningxen.com

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