Accuracy/reliability of "top" CPU usage numbers

Cathey, Jim jcathey at ciena.com
Fri Nov 14 16:15:32 UTC 2014


Things like 'top' have _always_ had issues with processes
that are clock-synchronized.  Very few OS's (and I don't
think Linux is one of them) actually account CPU time
by use of things like the PPC TBR register (for example).
Most do it via statistical sampling in a clock interrupt.

The top-analog we had on our OSE products was _very_ accurate,
because it accumulated CPU consumption via the TBR deltas
on context switches.

-- Jim



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