Linux（Ubuntu）的平均负载高于总真实利用率？

I have a dell pd2950(2x4core) server running Ubuntu server 12.04LTS. And there's a VLC encoder instance running. Recently I updated the script(VLM) for VLC to increase quality and this means I'm increasing the CPU utilization too. So I started to tune the script to avoid exceeding maximum utilization. I use I have a dell pd2950(2x4core) server running Ub