Re: [ECOS] Re: DSR Scheduling Problem

[Dirk Husemann <hud at zurich dot ibm dot com>]

Grant Edwards wrote:

> On 2006-01-14, Jay Foster <jay@systech.com> wrote:
>
>  
>
> > I still think that FIFO queuing of the DSRs is better than
> > LIFO queuing, because in the absence of any DSR priority
> > information, the best that can be done is temporal priority
> > (ie FIFO).
> >    
>
> That happens to work for your application, but I don't see how
> you can say that FIFO is best in the general case.
>  
hmm...i think jay has a point here: we are apparently loosing temporal 
ordering --- so even if a system would be capable of handling the load 
if the DSRs were executed in the order the associated ISRs occurred, 
with the current LIFO implementation it fails --- as demonstrated by jay.

>  
>
> > This prevents the case (that I'm seeing) where a lower
> > priority ISR's DSR preempts a higher priority ISR's DSR (the
> > priority is lost in the LIFO DSR queue).
> >    
>
> I still maintain that your application is either broken or you
> don't have enough CPU.  If one interrupts source requires so
> much DSR time that others can't run, then there is simply
> something wrong.  You seem to prefer a tx underrun error to an
> rx overrun error.  I guarantee you're going to get one or the
> other.  On the systems I work on, either is equally fatal, so
> it is not the case that FIFO is better than LIFO.  Both work
> equally well.
>  
hmm...apparently jay is seeing neither of your predicted results since 
he switched to FIFO...

--
Dr Dirk Husemann, Pervasive Computing, IBM Research, Zurich Research Lab
	hud@zurich.ibm.com --- http://www.zurich.ibm.com/~hud/
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