[CentOS] "near native" performance with xen?

Daniel de Kok danieldk at pobox.com
Mon Aug 6 20:21:44 UTC 2007


On Mon, 2007-08-06 at 14:55 -0400, Johnn Tan wrote:
> Assigning all the VCPUs.

Having more than one vcpu currently emits non-fatal error messages, at
least with the C5 domU kernel. I didn't have time to look into that yet.
Though, it's probably useful for threaded applications if it works. Note
that you can always specify which CPUs can be used by a domU (seen from
the hypervisor), regardless of the number of vcpus. E.g.:

cpus="0-1"
vcpus=1

>  And as much RAM as you can get away with (maybe leaving the dom0 with 512MB).

The Xen hypervisor requires 64MB RAM. If you don't do much work in dom0
you can set the dom0 memory fairly low. I have seen people setting it to
64 MB RAM. But remember that this is the minimum, suppose that a system
has 1024 MB RAM, and only one 512MB domU guest. dom0 can use
approximately 1024 - 512 - 64 = 448MB RAM, even if dom0-min-mem is set
to 64.

> But are there others? Since I'm doing paravirtualization, I 
> assume I don't need to turn on VT in the BIOS?

No.

>  What about 32-bit v. 64-bit OS, for the dom0 and for the domU? (I'll be 
> using CentOS-5.) Anything else?

A 64-bit dom0 with 32-bit domUs isn't currently supported in CentOS 5,
but it it will in 5.1.

-- Daniel




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