[CentOS-virt] Xen network problem

Fri Oct 30 19:26:35 UTC 2009
Ken Bass <kbass at kenbass.com>

I have a machine with 8 CPU's (2 quad xeons). (Centos 5.4 currently).

Currently, I am running 2 domUs. One with 4 CPUs and another with 2. 2 
remain unused. I am using routed networking.

On the one machine with 4 CPU's, there is a cronjob at 4am which 
utilizes the CPU/disk pretty heavily. It is rebuilds a mailing list 
archive (using MHonarc) and rebuilds a search engine index (swish-e). I 
dont think it uses more than 1 CPU though because the index rebuilding 
is not multi threaded, as far as I know.

This cron runs at 4am each day and takes about 7 minutes. My ISP is 
telling me that their alarms are going off because they cannot ping my 
server between 4am and 4:07am.

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!