Arch Linux

pradtf

Member

Registered: 2009-06-10

Posts: 149

SOLVED low latency kernel: am i running RT?

following this item recommended on the rosegarden elist:
https://cm-mail.stanford.edu/pipermail/ … 18882.html

i try to get the RT kernel working:

preempt=full
at bottom of /etc/defaults/grub
do sudo grub-mkconfig -o /boot/grub/grub.cfg
reboot

sudo dmesg | grep -i preempt
Dynamic Preempt: full

play things on rg - perfectly! no issues with timidity.service running.
before doing this i'd get crackles and pops, so i presume that rt is working.

then i try to go back, by commenting out the preempt=full line
do sudo grub-mkconfig -o /boot/grub/grub.cfg
reboot

but still see
Dynamic Preempt: full
in dmesg

BUT when i play, i get the same crackles and pops, so no RT?

1. shouldn't it say something other than Dynamic Preempt: full?

on the wiki it says:
"Since a while ago, the stock Linux kernel has proven to be adequate for realtime uses. "
https://wiki.archlinux.org/title/Profes … ime_kernel

however, in my situation, it seems that putting
preempt=full
in grub does make a difference.

2. however, is this the proper way to turn on|off RT?
or should i be looking at linux-rt stuff from AUR?

3. is there any reason not to RT all the time even when not doing pro-audio?

Last edited by pradtf (2022-06-07 19:32:10)

---

in friendship,
prad

Maniaxx

Member

Registered: 2014-05-14

Posts: 760

Re: SOLVED low latency kernel: am i running RT?

'preempt=full' is a kernel parameter. You'd append that to 'GRUB_CMDLINE_LINUX_DEFAULT'. But its not necessary as 'full preemption' (as you already noticed) is 'full' by default (on a PREEMPT_DYNAMIC configured kernel).

Beside that, you could add 'threadirqs' as a parameter. It should help to improve latencies even further (see here). If that works good enough for you there shouldn't be any need to run a dedicated RT kernel.

'Realtime' measures might come at the cost of some throughput of the kernel. I run it as a daily driver. Not sure about the real impact.

Last edited by Maniaxx (2022-06-07 18:50:16)

---

sys2064

pradtf

Member

Registered: 2009-06-10

Posts: 149

Re: SOLVED low latency kernel: am i running RT?

@maniaxx
thx for this info!

i tried preempt=none and found some crackles and pops.
putting in threadirqs didn't make much difference compared to the default, possibly because i'm running on an i7. may be on a weaker machine the differences will be more evident, so i might give it a try there too.

appreciate the help and will mark solved!

---

in friendship,
prad