Difference between nice ps and top commands

[neil al]

Thanks for the info.

On 6/16/06, Alan McKinnon <alan at linuxholdings.co.za> wrote:
>
> On Thursday 15 June 2006 10:01, neil al wrote:
> > Hi,
> >
> > May I know what is the difference between the 'nice ps -eo
> > pid,user,time,%cup%' and 'top' command. For example when i run a
> > tomcat servlet container the nice ps -eo pid,user,time,%cup%
> > command will print java process has a very large cpu usage and on
> > the other hand, when try the top command the java process has
> > little or no cpu usage. Both commands have different output values.
>
> ps and top are not displaying the same thing, even though the use the
> same name for them.
>
> From the ps man page:
> CODE  HEADER  DESCRIPTION
>
> %cpu  %CPU    cpu utilization of the process in "##.#" format.
>               Currently, it is the CPU time used divided by the time
>               the process has been running (cputime/realtime ratio),
>               expressed as a percentage. It will not add up to 100%
>               unless you are lucky. (alias pcpu).
>
> From the top man page:
> k: %CPU  --  CPU usage
>    The task's share of the elapsed CPU time since the last screen
>    update, expressed as a percentage of total CPU time.  In a true SMP
>    environment, if 'Irix mode' is Off, top will operate in 'Solaris
>    mode' where a task's cpu usage will be divided by  the  total
>    number  of  CPUs.   You toggle 'Irix/Solaris' modes with the 'I'
>    interactive command.
>
> So ps calculates cpu usage by using the entire time the process has
> been running giving a broad average over time. top considers only the
> last second (by default), which can be very different from the ps
> value under heavy load.
>
> Analogy: consider a Formula 1 car. It does 200mph down the main
> straight - this is top. It also covers the 200 mile race in 1h30min,
> and average of 133 mph - this is ps
>
> --
> If only me, you and dead people understand hex,
> how many people understand hex?
>
> Alan McKinnon
> alan at linuxholdings dot co dot za
> +27 82, double three seven, one nine three five
>
> --
> ubuntu-users mailing list
> ubuntu-users at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/ubuntu-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.ubuntu.com/archives/ubuntu-users/attachments/20060616/32357f57/attachment.html>