On 6/6/20 8:35 pm, Jeremy Jongepier wrote:
On 04/06/2020 11:25, nik@xxxxxxxxxxxxxxx wrote:
Hmm I never felt any advantage using RT kernels, either, at least in the recent
years, so I wonder if they still have any advantage in 2020 ? And that's not a rhetorical
question, I really wonder what contemporary use cases for RT kernels in the audio world are.
I feel like these kernel-tuning approaches date back to times when desktop responsiveness
etc. were much more serious issues. Might be wrong here, of course.
I concur that with some applications a RT kernel can be beneficial,
think of running soft-synths or samplers at very low latencies (with
buffer sizes below 128 samples) or for use with dedicated devices like
MOD Duo, Zynthian and that TC Electronics device that passed here a
couple of days ago.
When using a DAW the benefits of using a RT kernel are less clear. Out
of curiosity I did some small tests with a 20 track Mixbus32C session
using ALSA at 128 samples buffer size, 3 periods and 48kHz sample rate
and with both a home-rolled 5.6.14-rt7 and a stock Ubuntu
5.3.0-lowlatency kernels the number of xruns stays below 5. Session is
about 3 minutes long and consists of a DrumGizmo Crocell kit and some
guitars running Guitarix, all real-time (so no bounced tracks). This is
on a somewhat older notebook with one of the first Intel i7 iterations,
a tweaked Ubuntu 18.04 (no hyper-threading, no Bluetooth, no Wifi) and a
decent USB sound card sitting on its own USB bus.
Thought I'd share it, maybe it helps people to decide if they should try
a RT kernel or not. For all a RT kernel is not a panacea that
miraculously solves your xrun problems, those problems could lie
elsewhere as already pointed out by others. Additionally to the Ardour
manual link I'd like to point to
https://wiki.linuxaudio.org/wiki/system_configuration. Even though it's
a somewhat older article it still contains valuable information that
could help pinpointing the cause of xruns.
Best,
Jeremy
That wiki article is a goldmine of good advice even if a couple of
things are outdated. Raboof's realTimeConfigQuickScan contains some
links back to it. The QuickScan script has recently been updated so is
100% useful again.
I started this thread so will report progress. I managed to compile
XanMod but it didn't perform well for me with a flood of xruns, probably
user error. Curiously the AVL lowlatency kernel didn't either which
doesn't seem right. So I ended up back with Liquorix which I've been
using all along, getting occasional random xruns which is what I was
trying to eliminate.
I just read some lengthy threads on Liquorix forum where its developer
damentz mentioned it is not actually targeted at low latency audio. It
is configured with CONFIG_HZ=250 and I'm wondering would it be worth
recompiling it with CONFIG_HZ=1000 as recommended several times in the
wiki article?
Roger
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