[LAU] rtirq configuration with external USB DAC?

al3xu5 / dotcommon dotcommon at autistici.org
Tue Aug 13 20:01:38 CEST 2019

Il giorno martedì 13/08/2019 19:06:33 +0200
Ralf Mardorf <ralf.mardorf at alice-dsl.net> ha scritto:

> you need to do your own research or wait that somebody else does chime in.

As I suspected... ;)

> However, here are my guesses, no hard facts:
> On Tue, 2019-08-13 at 17:11 +0200, al3xu5 / dotcommon wrote:
> > Can you tell me why they shoud be removed now, please?  
> https://www.rncbc.org/drupal/comment/6553#comment-6553

Thank you. Also I have read at:


...and now thinga are clear enough.

> Regarding timer usage there are anyway a lot of myths and no clear source of
> information. RTC vs HPET (HR timer) vs TSC. While TSC should be the best
> source, some information claims that TSC could suffer from pitfalls that
> render it useless.

I know it is a mess...

I should have the cpu governor set to performance (no idle):

me at arrakis:~$ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

and timers:

me at arrakis:~$ ls -l /dev/rtc0
crw-rw---- 1 root audio 253, 0 ago 13 18:15 /dev/rtc0
me at arrakis:~$ ls -l /dev/hpet 
crw-rw---- 1 root audio 10, 228 ago 13 18:15 /dev/hpet

That should be ok I think.

> I set up Qtractor to use the default timer as the MIDI queue timer, so it
> should be TSC. MIDI is independent from audio, but I suspect it's better, if
> audio and MIDI are using the same timer.

Not using MIDI...

I am using a audio workstation to record (so I need low latencies with
possibly no xruns), plus a playback audio server for my hifi system, with a
an external USB2 DAC (here I need a clear audio signal with a "precise" clock

> IIRC the keyboard driver was added, since some people experienced the
> keyboard being unresponsive, but I might be mistaken.

Ah, yes this seems a good explaination... 

> > Also, consider now I am using rtirq-init version 20150216-2... There is a
> > newer (better) version I should use with a sysv-init (NO systemd) machine?  
> I don't know. In the paste some versions of rtirq didn't fit to some kernel
> versions. There were mismatches with the names in the RTIRQ_NAME_LIST, when
> using a brand-new kernel with some of that time current rtirq scripts years
> back, when the rtirq scripts were written for previous kernel releases of
> that time.

Thanks again. I have found this new release:

I have manually extracted and installed the sysv-init script on my system
(4.6.0-0.bpo.1-rt-amd64) and it seems to work fine.

Finally I have simply set:

RTIRQ_NAME_LIST="rtc0 usb1"

and priorities are as expected.

Thank you a lot.


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