I've seen a few posts similar to this, most notably here, but wasn't quite satisfied with the answers. I'm comparing top and ps results on a specific process and see huge discrepancies in CPU usage. top varies between <1% and 100% from interval to interval including periods of sustained highs (>50% for 3-4 intervals), while ps is steady at 2.2%. The process I'm watching doesn't have any children or anything, so I'm not quite sure what to make of it. Since there are sustained high periods in top, I feel I can rule out sampling interval.
Is this really just a discrepancy in how these two tools handle I/O wait time, as suggested by the question I linked to above?
EDIT:
I've seen it fluctuate to 2.1% in ps, but that's it so far. Output from top -p 4522:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
4522 root 16 0 340m 316m 4732 R 54.7 1.3 508:57.46 maui
Output from ps u -p 4522:
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 4522 2.2 1.3 348764 324456 ? Ss Aug25 509:25 /usr/local/maui/sbin/maui
The likeliest reason is that top shows the percentage values as a percentage of a single CPU while ps shows the percentage of total available CPU power. Try running top and hitting ShiftI while it's running to show the percentage of all cores.
If this is a server cluster with a lot of CPUs, what you describe is normal behavior. Also see here.
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