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    SubjectRe: how to set priority for idle process ?
    On Apr 11, Greg Alexander wrote:

    > > what's the best way to set the process priority (2.0.x kernel)
    > > for a process which should *not* compete (or as less as possible)
    > > with user processes running with "nice 19" ?
    >
    > Could you do "nice 20"?

    nice 20 is the same as nice 19 (check ps output).

    > Regardless, everything should compete equally if on
    > the same niceness level. if the user doesn't want competitors to win the
    > timeslice battle, they shouldn't nice themselves down that much.

    I want to have 3 possible classes of applications/processes running:

    1) interactice work
    2) background comptations & batch jobs
    3) idle task

    and I'd like that the higher priority get *every* CPU time needed and
    they shouldn't need to compete with lower priorities at all (some kind of
    fixed priority scheduling).

    running 3 jobs with nice 0, 10 and 19 give the following distribution
    of CPU time:

    PID USER PRI NI SIZE RES SHRD STAT %CPU %MEM TIME COMMAND
    480 root 17 0 816 56 28 R 61.6 0.1 0:37 idle
    479 root 18 10 816 56 28 R N 31.9 0.1 0:19 idle
    478 root 20 19 816 56 28 R N 5.0 0.1 0:03 idle

    so the interactive job looses ~40% cpu time due to background jobs.
    only running background and idle jon (nice 10 and 19) gives

    PID USER PRI NI SIZE RES SHRD STAT %CPU %MEM TIME COMMAND
    483 root 18 10 816 56 28 R N 85.9 0.1 0:52 idle
    482 root 20 19 816 56 28 R N 12.5 0.1 0:08 idle

    so the idle task still uses 12% CPU while it shouldn't as there are
    more important jobs around...



    Harald
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