Re: [linux-audio-dev] priority inversion & inheritance

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Subject: Re: [linux-audio-dev] priority inversion & inheritance
From: Martijn Sipkema (msipkema_AT_sipkema-digital.com)
Date: Thu Jul 11 2002 - 17:21:00 EEST


> [constant nframes]
> > But why is this needed? The only valid argument I heard for this is
> > optimization of frequency domain algorithm latency. I suggested a
> > capability interface for JACK as in EASI where it is possible to ask
> > whether nframes is constant. The application must still handle the case
> > where it is not.
>
> For freq domain stuff its not an optimisation, if the constant CPU time
> per process() requirement is to be met it is a requirement.

But is constant CPU time per process() a requirment? It is only an optimum
IMHO.
When doing large (more than one period) FFTs this will not be possible. So
the requirement is never in any callback use more CPU time than is available.
This also means that hardware that would use callbacks for which the time
available for process() is mucj smaller than the time (data) process() is
called for is a bad design. Note that this is not the case for the constant
rate interrupt audio hardware (allthough it still arguably is a bad design).

> Eqally we could add a buffering FIFO to hypothetical cards which produce
> non constant frames per period. I think this would affect far fewer
> people.

Perhaps, but it would affect them all the time. Also this buffer would have
to be fairly large relative to the hardware buffer in order to not have the
samples to process/time to process fluctuate too much.

--martijn

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