Subject: Re: [linux-audio-dev] Realtime restrictions when running multipleaudio apps .. Was: Re: disksampler ...
From: Benno Senoner (sbenno_AT_gardena.net)
Date: Tue Jul 18 2000 - 20:38:39 EEST
On Tue, 18 Jul 2000, Erik Steffl wrote:
> >
> > Thus, a realtime soundserver must somehow allow in-process execution, so
> > that the realtime parts of apps can be gathered inside the soundserver.
>
> crash of an application that runs inside of soundserver would crash
> soundserver, which in turn causes the crashes of all sound applications.
> how do you get around that?
you have to live with that and in the professional world, a crash of a
single soundmodule means making your recording useless.
For realtime we simply have to live with this crash-problem.
At least we do not get a complete system lockup but only a simple
segfault.
David said you could add some memory protection to via a kernel module.
But that is too tricky IMHO.
>
> you could prevent the application crash (but every application would
> have to be aware of crashing sound server) but I don't see any workable
> way to prevent the audio server to crash.
>
> isn't shared memory for data communication fast enough?
shared mem is the fastest you can get and it is encouraged to use this
form of communication as much as possible, but the problem are
the scheduling timings , process priorities , blocking times
when waiting for data on unix pipes , sockets etc.
The goal is to be able to deliver 2.1msec latencies for the whole
"studio", thus we have to live with 700usec ( 0.7msec!) fragment times with
occasional spikes to max 1.5 1.8msec in order to avoid any dropout.
And that is a damn short time ... we can achieve it only using the mentioned
"manual scheduling". As soon as the OS gets in the way with multiple processes,
sockets, unix pipes etc, we have no guarantee anymore that we will complete
our job in time.
But no one requires you to convert/run all your apps within this model.
Only the high-end ones will require so.
(I think Cubase + ReWire on windows does it in a similar way)
Benno.
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