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!
----- "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. -- Christopher G. Stach II