Re: [ECOS] Re: DSR Scheduling Problem

[Sergei Organov <osv at javad dot com>]

Brett Delmage <brett@twobikes.ottawa.on.ca> writes:

> On Mon, 13 Feb 2006, Sergei Organov wrote:
>
> <nice analysis deleted>
>
>> Overall, the above analysis suggests LIFO is never better than FIFO and
>> it could be much worse than FIFO.
>> 
>> Isn't it time to finally get rid of LIFO wait queues in eCos? Any
>> objections?
>
> Isn't ECOS about choice?

Well, unfortunately choice doesn't come for free. More testing, more
opportunities for bugs, more confusion, etc. I believe useless choices
are evil.

> Make this configurable option and allow users to try both. :-)

Which of the options do you suggest to be the default? How do you
explain users the criteria to choose one algorithm or another? How will
user compare the choices in his tests when most of time the algorithms
behave exactly the same? How do you explain why LIFO choice is there in
the first place if it has no advantages?

For example, the "array" choice for DSR queue does have an excuse as
being interrupts-disable-free, and it has an excuse of not being the
default as it has potential problems with missing DSRs. What's an excuse
for keeping LIFO choice? The only one I see is backward compatibility,
but due to the fact that eCos never specified exact order of DSRs it
shouldn't matter.

-- Sergei.

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