Re: [PATCH] scheduler patch, faster still

Albert D. Cahalan (acahalan@cs.uml.edu)
Mon, 28 Sep 1998 16:56:11 -0400 (EDT)


yodaiken@chelm.cs.nmt.edu writes:
> On Mon, Sep 28, 1998 at 11:01:43AM +0200, Rik van Riel wrote:
>> [somebody wrote]

>>> I'm very skeptical of loose use of the term RT.
>>> Are these tasks of yours really RT? Hard? Soft? Statistical?
>>
>> They are fairly hard and are triggered from an interrupt. After
>
> "Fairly hard" means absolutely nothing at all.

You could say the same for "hard" and "soft", since I've seen several
different definitions. He could give a better answer if you asked a
better question.

Does "hard" mean human life is involved? What about large sums
of money? (and define "large" too if that is the case)

Maybe the system is not a boolean problem. You could lose money at an
exponential rate, 2**n $ for every microsecond past your deadline.
The number of people killed could rise with the square of the time
after you miss your deadline, with a 0.1 second delay meaning 0.034
people killed on average and a deadline that you fully expect to miss.

It's all statistical. There is a cost of failure (annoyance, money
lost, billions die gruesome deaths, your mom dies a gruesome death...)
which determines the amount you are willing to pay for a solution.
Solutions vary in cost and in risk of failure.

You could call a 0.001 chance "soft" and a 0.00000001 chance "hard".
Whatever... They are terms you have to define.

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