Xen users - May 2006 - VCPUs with many (20?) domains

My question is about the stability (maturity?) and performance of the
VCPU feature in Xen3.

I have a quad core (dual dual core) Opteron box with 8GB of RAM (4x1GB
per CPU) which is going to host about 20 (lets say) domU''s. The
domU''s
are likely to be LAMP servers.

At the moment I''ve got the default Xen setup where there is 1VCPU per
domain. I am wondering if it is better in terms of performance to
change this to 4VCPUs per domain or if this will detrimentally affect
the overall performance of the domains as a whole.

Anyone have any hints / suggestions / ideas?

Thanks
-Rob

-- 
------------------------------------------------------
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"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
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> Anyone have any hints / suggestions / ideas?
Yep. VCPU 0 will take a huge it for I/Os as they are not well balanced. So just
make sure you balancer all your VPCU 0s on as much physical CPU as you can.

Unless you have huge needs for processing power into domUs, I''m not
sure you''d benefit from 4 VCPUs par server. Having two of them would
balance I/O on VPCU 0 and processes will still be able to run in parallel on
VCPU 1. Could be a nice deal.


BR,

--
Sylvain COUTANT

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