rt kernel

Ralf Mardorf ralf.mardorf at alice-dsl.net
Wed Apr 6 10:54:17 UTC 2011

On Wed, 2011-04-06 at 12:14 +0200, Alessio Igor Bogani wrote:
> Dear Ralf,
> 2011/4/6 Ralf Mardorf <ralf.mardorf at alice-dsl.net>:
> [...]
> > Note that today we should prefer the tickless timer.
> [...]
> > The 1000 Hz timer still isn't obsolet, because HPET/HR timer sometimes
> [...]
> How have you tested? What results have you obtained? If you want
> convince someone else you should provide testing procedures and
> numeric results.

If I play a MIDI track with external MIDI equipment, DX7, Matrix-1000,
D4, TG33 and others with 1000 Hz timer and record it to an audio track
and watch the files by Audacity, I can see that there's more jitter,
than when using the HR timer.
I also recorded kick, hi hat and snare one after the other and the
rhythm didn't groove anymore.
On LAD, 64 Studio lists, perhaps JACK devel and others too I posted
tests years ago. All regarding to this issue and other sync issues,
because Linux lacks on sync.

> [...]
> > What is my point?
> >
> > RT on Linux isn't 'hard RT', so de facto even the RT patch isn't a real
> > RT patch.
> I think that no one here is  interested to determine how much the
> PREEMPT_RT patch is "hard" or "soft". We are working on a kernel that
> better fits our users needs.

Soft real-time isn't usable for good music. This is an issue for every
PC OS (not for oldish computers like the C64 or Atari ST, they are hard
real-time capable). Of cause, comparing Steinberg and Linux by a MIDI
file on the same machine, it's audible that Linux is far behind a
Steinberg PC. I did test this on my computers a long time ago and can't
repeat this tests, because I don't like to install Windows again.

> In any case the -rt/-realtime kernel maintainer role is vacant. Are
> you interested?

Hm? I guess I don't have enough knowledge to do that, OTOH I've seen
repositories with RT kernels where debugging options where enabled, that
warned to 'slow down' real-time.

AND I'm not able to build the kernel-rt in a way, that I can add the
proprietary NVIDIA graphics driver.

I'm thinking of writing a better script to build the next kernel RT and
to post it again.

> Ciao,
> Alessio



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