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us = user mode
sy = system mode
ni = low priority user mode (nice)
id = idle task
wa = I/O waiting
hi = servicing IRQs
si = servicing soft IRQs
st = steal (time given to other DomU instances)
S(tate)
D Uninterruptible sleep (usually IO)
R Running or runnable (on run queue)
S Interruptible sleep (waiting for an event to complete)
T Stopped, either by a job control signal or because it is being traced.
W paging (not valid since the 2.6.xx kernel)
X dead (should never be seen)
Z Defunct (“zombie”) process, terminated but not reaped by its parent.
https://www.andymillar.co.uk/blog/index.php/2006/12/24/geekery/linux-load-average-explained/
http://www.linuxjournal.com/article/9001