On Fri, Sep 24, 1999 at 10:39:06AM -0500, [EMAIL PROTECTED] wrote:
>
> I set an 30hz simulation application to SCHED_FIFO and set priority to 98 but
> "top" shows the priority oscillating between 14 and 20. The R/T app intially
> show priority of 14 and slowly climb to 20, then top will climb from 11 to 19,
> then both reset back to 14 and 11 and the cycle repeats. What is the
> relationship between sched priority and thhe priorities show by top?
>
> I am running Redhat 5.2 (2.0.36) and RTL 1.1 is used to generate the 30Hz via a
> FIFO.
>
These are "niceness" values, which are the scheduler's method of determining
which task should be run. As a general rule, it runs the task with the highest
niceness value for a timeslice, and then subtracts a penalty from its niceness,
which may or may not cause a different task to run. Meanwhile, tasks that are
not given timeslices have their niceness increased, so that they eventually
run.
However, this is only for SCHED_OTHER. SCHED_FIFO follows different rules,
the rules you expect for the SCHED_FIFO scheduling class. However, probably
in order to avoid polluting the fast patch in the scheduler, niceness values
are computed for all tasks, including SCHED_FIFO, even though they are not
used.
dave...
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