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List:       linux-rt
Subject:    [rtl] 1 msec timeslices in Linux scheduler
From:       steve rosenbluth <stever () la ! creatureshop ! henson ! com>
Date:       1998-12-28 18:02:46
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-- 
Steve Rosenbluth
Jim Henson's Creature Shop
2821 Burton St, Burbank CA
(818) 953-3030
["1msec-rtl.txt" (text/plain)]

This is a clarification of my previous message:

I havent found any way to force a linux user space process to run immediately 
after my real-time IRQ handler. I'm trying to decrease the timeslice duration 
in Linux so my soft real time app has a faster response to what the real time 
handler has done.

How can I force the linux kernel scheduler to give processes only 1 millisecond
maximum per timeslice ?

I have changed the HZ variable in param.h from 100 to 1000, and my
rt-2.0.35 kernel runs fine.

This is the linux process which should show me the duration of my new linux 
timeslices: 

int main(void)
{
  if (ioperm(LPT, 8 , 1) < 0) {
      fprintf(stderr,"ioperm: error accessing IO-port. Root Privileges required\n");
      exit(-1);
  }
  while(1) {
      outb(0,LPT);
      usleep(1);     /* here we get scheduled away */
      outb(1,LPT);
      usleep(1);    /* here we get scheduled away too */
  }
    return 0;
}

I see (on an O-scope) my process runs every 2 msec, (as opposed to every 20 msec 
when HZ was 100). Why doesn't this process run every millisecond ? !!!

I tried changing DEF_PRIORITY in sched.h from (20*HZ/100) to (10*HZ/100)
but this apparently didn't have the effect I wanted: my O-scope still
shows 2 msec timeslices. (I admit I don't know how DEF_PRIORITY is used
in the linux scheduler.)

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