Re: [LAT] [LAU] Are RT-patches needed anymore? (Was Re: >= 2.6.27 RT ETA?)

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To: dieeasy <dieeasy.moo@...>
Cc: <linux-audio-tuning@...>
Date: Tuesday, February 3, 2009 - 6:11 pm

On Tue, 2009-02-03 at 16:04 +0100, dieeasy wrote:

Jack will give SCHED_FIFO to just the audio thread of the client
application (which is normally the only one that actually needs that).

> - how can I identify the audio thread and change scheduling/nice

I don't think you can. You can see the threads and their pids
in /proc/PID/task/ but you don't know which is which. They are just
numbers.

I pays to have jack applications that are properly designed. Then you
don't have to worry about scheduling and priorities (in a properly
configured system).

> - given audio threads already are highest priority, isn't it better to

Audio threads should be the only ones that need realtime scheduling.
What do you mean by "all audio processes"?

> - apart from irq threads, is there any other big improvement a -rt

The time kernel system calls spend in a non-preemptible state are
supposed to be lower than in a stock kernel (but the gap has been
getting narrower). That means that a process that is ready to run and
has SCHED_FIFO has a better chance of being scheduled in time, in the
stock kernel there could be delays in scheduling that cause the process
to be scheduled too late... (and you get an xrun)

> - does enabling "preempt RCU" make a big difference?

I have no idea...

> Sorry if some questions are trivial or already got answered somewhere

SCHED_RR will be preempted when it uses up its time slice. That prevents
lockups but it means you could get an xrun anyway.

> [2]

I would assume that's how it works.

You don't want the whole app to be SCHED_FIFO, that would mean that, for
example, screen updates would potentially starve the audio threads.

> [4] I use "stock" debian kernels reconfigured with forced

Latest kernels are known to be pretty good without the rt patch. Is this
2.6.28.*?

-- Fernando

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Messages in current thread:
[LAT] Hello, Gilberto Borges, (Wed Jul 30, 9:39 pm)
[LAT] Hyper Threading, Jaromír Mikeš, (Wed Sep 17, 10:43 pm)
[LAT] amd64: kernels? base system?, james of jwm-art net, (Tue Dec 2, 5:53 pm)
Re: [LAT] [LAU] Are RT-patches needed anymore? (Was Re: &gt;..., Fernando Lopez-Lezcano, (Mon Feb 2, 11:08 pm)
Re: [LAT] 2.6.29-rt1, Robin Gareus, (Sat Mar 28, 1:18 pm)
[LAT] RT kernel for audio and dynamic vs static ticks, Lars-Erik Helander, (Mon Jan 18, 12:50 pm)
Re: [LAT] 2.6.29-rt1, Fernando Lopez-Lezcano, (Sat Mar 28, 6:11 pm)
Re: [LAT] 2.6.29-rt1, Ray Rashif, (Wed Apr 8, 2:54 am)
Re: [LAT] [LAU] Are RT-patches needed anymore? (Was Re: >..., Fernando Lopez-Lezcano, (Tue Feb 3, 6:11 pm)
Re: [LAT] amd64: kernels? base system?, Daniel James, (Wed Dec 3, 11:17 am)
Re: [LAT] amd64: kernels? base system?, james of jwm-art net, (Wed Dec 3, 3:29 pm)
Re: [LAT] Hyper Threading, Robin Gareus, (Thu Sep 18, 2:53 pm)
Re: [LAT] Hyper Threading, Jaromír Mikeš, (Thu Sep 18, 7:45 pm)
Re: [LAT] Hello, Andy Farnell, (Wed Jul 30, 10:00 pm)
Re: [LAT] Hello, Marcos Guglielmetti, (Wed Jul 30, 11:00 pm)
Re: [LAT] Hello, Daniel James, (Tue Aug 5, 3:12 pm)
Re: [LAT] Hello / kernels, Marcos Guglielmetti, (Wed Aug 6, 8:53 am)
Re: [LAT] Hello / kernels, Robin Gareus, (Thu Aug 7, 5:05 pm)
Re: [LAT] Hello / kernels, Marcos Guglielmetti, (Wed Aug 6, 3:36 pm)