[LAU] Realtime latency kernel testing

[allcoms]

Thanks Robin for your massively useful tips there on how to (stress) test
JACK - I think what you just said, in an edited form, should be included on
the JACK FAQ page please Paul!


On Sun, Dec 12, 2010 at 12:41 PM, Robin Gareus <robin at gareus.org> wrote:

> On 12/12/2010 01:03 PM, ailo wrote:
> > I've been looking around for any tests made comparing the different
> > kernels, -rt, generic, or any other type of realtime enchanced kernel.
> > I haven't found any test results yet, at least none audio related. I did
> > find some testing tools at rt.wiki.kernel.org, but don't know if and how
> > they could be made relevant to audio low latency testing.
> >
> > I suppose the most interesting results would come from testing different
> > kernels with jack/alsa and jack/ffado.
> >
> > Has anyone done such tests?
>
> It is not trivial to perform such tests and AFAIK there's no benchmark
> suite to automate the process.
>
> There are a few tools to test JACK's realtime performance:
>
>  - the ardour-source includes `tools/jacktest.c` checks for the max DSP
>   load at which an x-run occurs.
>
>  - http://wiki.linuxaudio.org/wiki/jack_latency_tests
>   git://rg42.org/latentor is a tool to automate measuring round-trip
>   audio latency iterating all JACKd -n/-p/-S parameters
>   However latentor is a pretty recent development and does not yet
>   report x-runs. We watch qjackctl's icon for now.
>
> AFAICT there's no recipe. It's a matter of knowing some internals about
> RT-linux to come up with a proper kernel .config and doing real-life
> tests. I think it is impossible to assign a number "suitability for
> pro-audio" to a kernel.
>
> For testing performance of the 64studio RT kernel: I do run a couple of
> heavy-sessions (e.g. 16 jconvolvers in a 16 track ardour session + jamin
> which procudes quite some DSP, system and IO load). If there's no x-run
> at 32fpp*2p/48kHz after 24 h while I to surf the web and read email and
> compile another kernel in the meantime I bless the build OK :) There's a
> few additional things: wifi, suspend/resume, freq scaling, etc on the
> checklist, too.
>
> 2c,
> robin
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>
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