12-08-2008
top command + %CPU usage exceeds 100%?
Hi there. I was looking at the output from running top and for short amounts of time, when I see all the process running and add up the values in the %CPU column the value exceeds 100% (I just add them quickly in my head). I assume that if I were to add up all my processes in the entire list, they still could not/should not exceed 100%. Is there some sort of explanation for this?
Thanks for any clarification.
-Carl
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LEARN ABOUT DEBIAN
cpulimit
CPULIMIT(1) User commands CPULIMIT(1)
NAME
cpulimit -- limits the CPU usage of a process
SYNOPSIS
cpulimit [TARGET] [OPTIONS...]
DESCRIPTION
TARGET must be exactly one of these:
-p, --pid=N
pid of the process
-e, --exe=FILE
name of the executable program file
-P, --path=PATH
absolute path name of the executable program file
OPTIONS
-b, --background
run cpulimit in the background, freeing up the terminal
-c, --cpu
specify the number of CPU cores available. Usually this is detected for us.
-l, --limit=N
percentage of CPU allowed from 1 up. Usually 1 - 100, but can be higher on multi-core CPUs. (mandatory)
-v, --verbose
show control statistics
-z, --lazy
exit if there is no suitable target process, or if it dies
-h, --help
display this help and exit
EXAMPLES
Assuming you have started `foo --bar` and you find out with top(1) or ps(1) that this process uses all your CPU time you can either
# cpulimit -e foo -l 50
limits the CPU usage of the process by acting on the executable program file (note: the argument "--bar" is omitted)
# cpulimit -p 1234 -l 50
limits the CPU usage of the process by acting on its PID, as shown by ps(1)
# cpulimit -P /usr/bin/foo -l 50
same as -e but uses the absolute path name
# /usr/bin/someapp
# cpulimit -p $! -l 25 -b
Useful for scripts where you want to throttle the last command run.
# cpulimit -l 20 firefox
Launch Firefox web browser and limit its CPU usage to 20%
# cpulimit -c 2 -p 12345 -l 25
The -c flag sets the number of CPU cores the program thinks are available. Usually this is detected for us, but can be over-ridden.
NOTES
o cpulimit always sends the SIGSTOP and SIGCONT signals to a process, both to verify that it can control it and to limit the average
amount of CPU it consumes. This can result in misleading (annoying) job control messages that indicate that the job has been stopped
(when actually it was, but immediately restarted). This can also cause issues with interactive shells that detect or otherwise depend
on SIGSTOP/SIGCONT. For example, you may place a job in the foreground, only to see it immediately stopped and restarted in the back-
ground. (See also <http://bugs.debian.org/558763>.)
o When invoked with the -e or -P options, cpulimit looks for any process under /proc with a name that matches the process name argument
given. Furthermore, it uses the first instance of the process found. To control a specific instance of a process, use the -p option
and provide a PID.
o The current version of cpulimit assumes the kernel HZ value 100.
AUTHOR
This manpage was written for the Debian project by gregor herrmann <gregoa@debian.org> but may be used by others.
cpulimit June 2012 CPULIMIT(1)