[CentOS] "near native" performance with xen?

[Johnn Tan]

Daniel de Kok wrote:
> 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.

What error messages are you seeing? On one of my machines, I 
have four domU's (kernel 2.6.18-8.1.8.el5xen), each with 4 
VCPUs. I don't see any errors in any of the domU's dmesg. 
But /proc/cpuinfo shows they are each using all 4 CPUs.

When I try to over-assign memory though, I definitely get 
errors and the domU is not created.


> 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.

Good to know. I'm a little hesitant to set it at 64MB, but I 
feel a little more comfortable now bringing it further down 
from the 512MB that I've been using as a dom0 minimum.


>>  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.

Yes, I'm looking forward to that, plus some of the other 
updates in 5.1.

But I'm curious whether 32-bit domU on 32-bit dom0 is more 
performant than 64-bit domU on 64-bit dom0. I'm about to do 
my own test of this sometime this week, but was wondering if 
others had already tried it.

johnn