Re: [aqualung-friends] -R, --realtime

[Mark K. <mar...@gm...>]

On 9/27/05, Tom Szilagyi <tsz...@us...> wrote:
> On Mon, Sep 26, 2005 at 04:37:25PM -0700, Mark Knecht wrote:
> > Running aqualung with the -R option, according to the help in Aqualung,=
 says:
> >
> > -R, --realtime: Try to use realtime (SCHED_FIFO) scheduling for ALSA
> > output thread.
> >
> > My question is does it cause problems for me to run the server
> > SCHED_RR if Aqualung is going to run SCHED_FIFO? Can jackd and
> > Aqualung run at different priorities and everyone be happy?
> > [...]
>
> Interesting question.
>
> First and foremost, I don't know if it's clear to you that the -R
> option of Aqualung works only for Alsa output. It has absolutely no
> effect if the program runs with OSS or Jack.

I did not know this. So if I'm running with only Jack, as I always do,
I should NOT use -R? This is different from alsaplayer and hence why
I've been doing what I do.

I've been learning a bit more about this on the ck-sources email list.

>
> In case of Jack output, the Jack server is the one that starts the
> Jack output thread running within Aqualung (as with any other
> Jack-ified program). This thread runs in the context of the Aqualung
> process, but it inherits its realtime and other attributes from the
> Jack process which actually started it.

Very interesting. I had no idea jackd did stuff like that inside your progr=
am.

>
> So to run Aqualung in realtime with Jack, just run Jack in realtime,
> and start Aqualung as usual (just as you start Ardour, etc.). No
> special options to Aqualung are needed (and there are in fact none).
>
> I think you may not necessarily see the realtime-ness of the Jack
> output thread in Aqualung when looking with tools such as ps or top,
> since it is a thread among other threads in a single process. AFAIK it
> depends on kernel versions whether threads count as separate processes
> on the OS level or not. Specifically, when running Aqualung on a
> 2.4.28 kernel I can see all 4 threads of Aqualung in top as separate
> processes (all named aqualung), while on 2.6.13 I only see *one*
> aqualung process. In this latter case, information shown by ps or top
> corresponds to the whole process and it is unclear to me as to what
> extent this reflects the attributes of one particular thread within
> the process.

OK, that explains a bit. I know there are some tools to see all the
threads on 2.6 kernels but I don't remember what they are. I'll go
look.

>
> The bottom line is that if Jack runs in realtime, and Aqualung has
> successfully connected to it, then it is in fact realtime (the Jack
> output thread, that is). If it were unable to run in realtime, Jack
> would have problems with it and starting up Aqualung as a Jack client
> would fail.

Is this what's happening when I run Jack at 64/2 and find Aqualung
telling me that the Jack server has shut down? It seems that when Jack
goes too fast Aqualung cannot get started.

Thanks,
Mark