Performance tuning is a sort of art. You know what you expect to reach, and you somehow strive towards that through selective tuning. Either your OS memory utilization, your network settings, NFS mount parameters, etc.
I’ve been to a customer who’s server acted funny. First, it had high load average – for an idle server with 2 CPUs, a load average which never gets below 1.0 can be considered high.
Viewing the logs I’ve seen lots of PS/2 error messages. It seems that the hotplug daemon had been very busy at respawning several times a second due to incorrect hardware detection – due to these PS/2 errors, and caused high load average (many processes in the CPU queue). Disconnecting the PS/2 port between the server and the KVM solved the issue, and within around 2 minutes the load average has decreased to around 0.02.
Hardware related problems are, usually, the most intensive and easy to solve performance hogging.