linuxaudio.org

On Tue, Jan 26, 2010 at 03:15:43PM -0500, David McClanahan wrote:
> 3. I'm a little worried about what some are calling realtime systems. The

quoted text
> realtime system that is part of Ubuntu Studio and others may be more

> preemptible than the normal kernel(as in kernel calls themselves can be

> preempted), but that's not a hard realtime system. A hard realtime

> system(simplistic I know) might entail a task whose sole job is to pump out

> a sinusoidal sound sample to the D-to-A on the sound card. A hard realtime

> scheduler would run that task at 44Khz no matter what. This would entail

> developing code that when the machine instructions were analyzed, would run

> in the time constraints(aka the 44Khz). RTLinux appears to be suitable and

> RTAI might be. Perhaps others.

That's not how Linux audio works. Processing is done in

blocks of typically between 64 and 1024 samples. 
> The way things are now even with the "realtime kernel" on U. Studio. , xruns

quoted text
> can occur because there's no hard limit on accessing resources-only

> priorities. This may work fine on newer/faster machines but not on the older

> ones. Some may say, "Go buy a faster machine". My answer is that won't

> necessarily solve the problem which is a proliferation of "systems" on top

> of systems without any assurance they'll all work together on time.

With current kernels you don't even need any RT patches

to get good performance, unless you need very low latency

(i.e. very small block sizes). I've been working most of

the day on a 64-channel system with several quite complex

apps, and I haven't seen a single xrun. Standard unpatched

2.6.32 kernel.

If you get xruns on a correectly set-up system (and that

requires very little these days) it's probably because

the apps you use have not been written in the way required

to perform well in a realtime context. Unfortunately there

are many like that.
Ciao,
--

FA
O tu, che porte, correndo si ?

E guerra e morte !

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