Re: [PATCH] [request for inclusion] Realtime LSM

Con Kolivas
2005-01-08T05:38:17Z

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Takashi Iwai wrote:
> At Fri, 7 Jan 2005 17:03:51 +0100,
> Arjan van de Ven wrote:
>>something like a soft realtime flag that acts as if it's the hard realtime
>>one unless the app shows "misbehavior" (eg eats its timeslice for X times in
>>a row) might for example be such a solution. And with the anti abuse
>>protection it can run with far lighter privilegs.
>
>
> This reminds me about the soft-RT patch posted quite sometime ago.
> I feel such a handy psuedo-RT scheduler class would be useful for
> other systems than JACK, too...

You've already proven that soft RT does not suit your requirements. The
current scheduler running a task at nice -20 has extremely long periods
of cpu availability at the expense of lower priority tasks and is close
to the behaviour you would get with a soft RT patch. Your concern is
exactly the scenario where nice -20 fails, and would be the same
scenario where a soft RT policy would fail. Doing this with a scheduling
policy, you want cpu time long after there is any hope for fairness or
safety of hanging. From experimentation with such soft RT policies, we
find average latencies can be reduced but the maximum ones, which are
the ones that concern professional audio, remain the same.

Cheers,
Con

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