[ECOS] Re: DSR Scheduling Problem

[Grant Edwards <grante at visi dot com>]

In gmane.os.ecos.general, you 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

True.

> --- 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.

I don't see how he's demonstrated that at all.   If you need to
run 150ms of DSRs in a 100ms time period, you're not going to
be able to run them all by re-ordering them.  Jay didn't
demonstrate that changing the order made all his DSRs run as
often as they needed to.  

>>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...

How do we know he's not getting tx FIFO underruns?

-- 
Grant Edwards                   grante             Yow!  .. I see TOILET
                                  at               SEATS...
                               visi.com            

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