From alsa-devel-owner@alsa.jcu.cz  Wed Jan 13 06:12:01 1999
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To: alsa-devel@alsa.jcu.cz
Subject: Re: Linux scheduler issues. 
In-reply-to: Your message of "Tue, 12 Jan 1999 12:57:17 +0100."
             <369B389D.FB567AB5@ife.ee.ethz.ch> 
Date: Wed, 13 Jan 1999 00:09:06 -0500
From: Paul Barton-Davis <pbd@op.net>
Reply-To: alsa-devel@alsa.jcu.cz
Sender: alsa-devel-owner@alsa.jcu.cz
Precedence: list

In message <369B389D.FB567AB5@ife.ee.ethz.ch>you write:
>Can you be more specific?

   [ ... good stuff from Tom elided ... ]

>Short of that (which can be avoided by not doing something silly), I
>can't see how your app can be preempted seriously, especially not
>by any other process.

   [ ... ]

>I can't quite see how anything of the above is a problem
>for audio apps that basically only burn CPU cycles and
>do IO to the soundcard (given a reasonable sound driver).

The assumption here, however, is that there is just one RT audio
process running. Although this may just be a real restriction that one
has to face (and realistically, its what happens on Windows and Mac
systems), as soon as there are two SCHED_FIFO or even SCHED_RR
processes, the guarantees offered by the scheduler in the single RT
process case seem to me to vanish. Once again, you need intense
cooperation between the processes to get things to work right.

As I say, that may just be realistic. But it would be *nice*, even if
not realistic, to think that I could run an efficient, non-GUI hard
disk recording application and a CPU-intensive realtime synth/audio
app like Quasimodo (or RTsynth or KDEsynth or whatever) and have the
right thing happen without both programs knowing about the other. At
the moment, thats hard to be sure of.

--p

