multitasking question

[mcollins at anchor.sps.mot.com]

Stan wrote:
> 
> Hi,
> 
> How to determine the CONFIGURE_MICROSECONDS_PER_TICK   and
> CONFIGURE_TICKS_PER_TIMESLICE value for optimal performance.?
> 
> At the present time, I use
> 
> #define CONFIGURE_MICROSECONDS_PER_TICK     833
> #define CONFIGURE_TICKS_PER_TIMESLICE       3
> 
> with 68000 (16 MHz).
> 
> What do you think about it?


Eric Norum replied:

> Offhand I'd say that 833 usec/tick is pretty fast for a 16 MHz 68000. 
> Your system will be spending a significant portion of its time
> entering/exitting/executing the clock interrupt handler.

  To provide some real-world info, I have been using the following
parameters on a 25MHz MC68331 board over the past few days:

      #define CONFIGURE_MICROSECONDS_PER_TICK   122

      /*
       * Timeslice interval is approx. 20ms.
       */
      #define CONFIGURE_TICKS_PER_TIMESLICE 164

  I've had as many as four tasks running simultaneously, three of which
can be pretty busy for short intervals, and have not apparently run out
of bandwidth.  Now I can't say that my configuration is optimal; the
numbers chosen were simply first guesses, however I would expect Stan's
configuration should work at 16MHz.

  On a related note, what is the best way to determine how a CPU's
bandwidth is being used within an application?  I've thought of adding
some diagnostic code to each task which drives an output signal high
while the task is running (this works for tasks which do something
then execute rtems_task_wake_after()) but I suspect there are probably
better methods.

					-- MC --
--
mcollins at wdc.sps.mot.com