multitasking question

[Joel Sherrill]

" (Michael P. Collins on korat)" wrote:
> 
> 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.

See cpuuse in libmisc. Alternatively, I have some gdb macros to 
do something similar.

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

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
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