[CentOS-virt] Xen network problem

Ben M.

centos at rivint.com
Fri Oct 30 20:34:54 UTC 2009

Not trying to take this off-topic, I think it is relevant.

Christopher: When I booted up with dom0-cpus 1, Windows 2008 could not 
"find" its second cpu. However, once up, I can "xm or virt-manager" it 
down to 1 cpu on cup 0 and everything is fine.

Is this a unique issue or do you have a tweak or hack to force smp with 
dom0 on one cpu?

Christopher G. Stach II wrote:
> ----- "Ken Bass" <kbass at kenbass.com> wrote:
>> It sounds like the domU is impacting the overall Xen performance. Is 
>> there anything I can do to tune this? It kinda defeats the whole Xen 
>> virtualization concept if a single CPU messes up the network. I am
>> going 
>> to try to add a 'nice' to the crontab for the 4am job, but still, 
>> something doesn't seem correct. Any suggestions would be much 
>> appreciated. Thanks!
> In high I/O environments or ones with a lot of unpredictable guests, it's a good idea to pin dom0's CPU(s) to physical cores and exclude those cores from the guests. I find that dom0 usually only needs one CPU (pinned to one core) in almost every environment. For example, on an 8 core box, dom0 gets CPU 0 (dom0-cpus 1) and all of the guests use 1-7. The occasional firewall/load balancer/something else high-I/O guest would also gets its own core, also excluded from use by the other guests, but you should avoid that until you find that it's necessary.

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