thomson@zazen.macc.wisc.edu (Don Thomson) (04/23/91)
I'm not sure how UNIX-generic the "top" program is, but its one of the main
tools we use to analyze performance on our DECstation 3100 running Ultrix 4.0.
We are trying to clarify the meaning of the percentage CPU time that is
displayed. We're looking at percentage idle and guessing that percentage CPU
time used + idle time should add up to 100%, but are rarely seeing CPU
percentages wander over 1 or 2%. I have a feeling we're comparing apples and
oranges here, so am looking for clarification of what exactly we're looking
at:
last pid: 8233; load averages: 0.64, 0.56, 0.00 12:03:09
59 processes: 55 sleeping, 1 running, 3 stopped
Cpu states: 5.2% user, 0.0% nice, 21.0% system, 73.8% idle zazen
Memory: 9536K ( 5360K) real, 27388K (17316K) virtual, 1296K free
PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
8213 thomson 25 0 612K 396K run 0:00 1.95% 1.95% top
8232 root 1 0 172K 64K sleep 0:00 0.39% 0.39% nntpxmit
21060 thomson 26 0 7828K 2648K stop 4:39 0.00% 0.00% emacs
The top man page says:
WCPU is the weighted cpu percentage (this is the same value that
ps(1) displays as CPU), CPU is the raw percentage and is the
field that is sorted to determine the order of the processes
and the ps man page says:
%CPU CPU utilization of the process. This is a decaying
average over a minute or less of previous (real) time.
Because the time base over which this is computed
varies since processes may be very young, it is possi-
ble for the sum of all %CPU fields to exceed 200%.
Can anyone help shed any light on exactly what kind of measurements we're
seeing here, and/or clarify the distinction between weighted and raw CPU
percentages? Thanks!
--
----- Don Thomson ----- MACC, 1210 W. Dayton, Madison, WI 53706 -------------
(608) 262-0138 thomson@macc.wisc.edu / thomson@wiscmacc.bitnet