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List:       linux-rt
Subject:    Minor Correction: Re:Tricky scheduling problem
From:       "Reinhold J. Gerharz" <rgerharz () erols ! com>
Date:       1997-09-01 14:34:18
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At 08:27 09/01/1997 -0400, W.Steenbeck Digital GmbH wrote:
>You are right.
>
>If you take a closer look at rt_prio_sched.c, you will see why. By
every
>call to rt_task_wait() for a
>periodic task the period will be added to the time of the last
scheduled
>wakeup !!not!! to 
>the time of now. This is used to get a more jitterfree timing. You
probably
>run into overload trouble in your application and should think of
splitting
>your sampling process-------- rt_fifo()------ or so.
>
>Jens

By adding the period to the last time scheduled rather than adding it
to "now," you get some assurance that your task will be scheduled,
say, 1000 (or whatever) times per second. Jitter cannot be controlled
because it depends on cache state, interrupt enable state, and the
number of cycles required to complete the currently executing
instruction when the timer interrupt occurs.
--
Reinhold J. Gerharz          http://www.erols.com/rgerharz/
PGP Key at http://www.erols.com/rgerharz/pgp/public-key.asc

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