Re: SCHED_DEADLINE as user

On 18/08/18 15:26, Tim Blechmann wrote:

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audio applications typically use SCHED_FIFO. however they are
rate-monotonic by design, so i wanted to evaluate how SCHED_DEADLINE
behaves here.

Right. Exactly what I started to think about lately as well.

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Asking because we might want to have a look at how to relax the current
privileges requirement.

please :)

Anything to try attracting new users. :-P

More seriously, could you please describe in a bit more details your
specific use case? Based on JACK I guess? Is it the application you are
interested into public available somewhere?

it could be based on JACK or natively on ALSA. furthermore the fun part
starts when trying to distribute work to multiple threads: during the
time slice of one audio callback (could be as low as 1.3ms), we need to
wake helper threads and (busy?)wait to collect all the results. (while
one of the applications is open source, it's not entirely
straight-forward to use)

for me it's more an investigation if SCHED_DEADLINE is actually feasible
in real-world audio application these days. tommaso used to have a
research prototype [1], built directly into JACK. however currently i'd
be more interested in using it in ALSA. but yeah, it's more an
investigation as SCHED_FIFO does a decent job for my use case ...

I (almost) see. Thanks for the details.

[1] http://retis.sssup.it/~tommaso/publications/LAC-2011.pdf

So, this was IIRC using AQuoSA hierarchical RT on EDF scheduler
implementation; which it was handy to easy the task of assigning CBS
server parameters to JACK clients (graph).

In your case - assuming you could already use DEADLINE for !root - do
you think you would need to use the same interface for the multiple
threads you are distributing work among? Or would you be fine with
assigning runtime/deadline for each one of those?

BTW, cc-ing Tommaso and Luca. Discussion started from
https://www.spinics.net/lists/linux-rt-users/msg19296.html