[linux-audio-user] kernel - using rtlimits, realtime_lsm

[Florian Schmidt]

On Thu, 22 Dec 2005 02:38:28 +0100
Sylvain Reynal <reynal at ensea.fr> wrote:

Hi,

> Florian,
> Is that to say that (cf. your tutorial, 
> http://tapas.affenbande.org/?page_id=6) reprioritizing IRQ handlers with 
> things like
> chrt -f -p 97 `pidof "IRQ sound_car_irq"`
> which prove so simple and efficient with an -rt kernel, are just pointless 
> with a preemptible kernel (assuming it was compiled with threaded IRQ 
> handlers)?

Which (compiling with threaded irq handlers) is only an option in a -rt
patched kernel. Vanilla doesn't have threaded IRQ handlers even in
"Preemptible Kernel" mode. Or so i seem to remember.

> That'd confirm my recent measurements, but still i can scarcely make out why 
> this is so.

I have no idea. I mostly only run Complete Preemption, which, when it
works, works great :) But from my understanding, unthreading the
soundcard IRQ handler or setting it to a high priority should be pretty
much equivalent from an enduser's point of view (Means: i have no clue,
but i bluntly assume). And at the time i actually used preemption modes
different from Complete Preemption for audio stuff, they were
equivalent. 

> And while we're at it, i get --amazingly enough-- far more xruns when 
> un-threading my PCI sound card IRQ handler (doing echo 0 > /proc/irq/...) 
> than when leaving it threaded... 

Hmm, this is weird. I'm not sure. It would be best to ask Ingo directly
about this. Might be a regression. 

Regards, Flo

-- 
Palimm Palimm!
http://tapas.affenbande.org