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!