Re: JACK 1: extreme CPU usage (since update from 5.0 kernel)

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On 2019-08-05 22:20:10 (+0200), Jeanette C. wrote:
> Hi David,
> thanks for your great and fast reply. I'd like to go through it, maybe
> we could delve into it together a bit more?
> Aug 5 2019, David Runge has written:
> ...
> > How do you start jack?
> My own systemd service as:
> jackd -R --timeout 4500 -d alsa -C cdelta -P pdelta -r 48000 -n 3 -p 256
> -z shaped
Hm, that sounds reasonable. Note, `-R` is the default and usually starts
jackd at RTPRIO 10.
On a realtime kernel you can set the maximum RTPRIO higher than the
lower halves (higher than 50) with the `-P` flag.
Check `man 1 jackd` for more info.

> > Is it the same with jack2?
> Never tried, since it's not been recommended for a long time and used
> to be heavily integrated with dbus.
Would be interesting to find out, whether you have the same issues there
as with jack(1).
The jack2 package also offers jackd, which should just work the same
with your service file (jack2 is a API compatible replacement).
Fun fact: The next jack2 release will offer a systemd user service out
of the box.
Also: Unless you have a bunch of GUI tools starting it via dbus
activation, the jack2 package defaults to launching jackd!

> Trying iotop, have to figure out a few settings for better
> readabililty with my braille display. Could be quite useful.
It's sometimes interesting to figure out, what's clogging the system.

> > You can try with linux-rt and/or linux-rt-lts.
> Do they also support schedutil, mostly my system is quite idle. :)
Yes.

> Regarding irqs: no shared irq, the soundcards are at 18 and 19. No
> rtirq not irqbalance. Would it help with that situation?
I guess irqbalance could improve your situation.

> > That's not a superlot of RAM, but you also don't have any hungry GUIs
> > :-)
> Definitely not! :)
> top
> ...
> KiB Mem :  3780140 total,   587016 free,   399196 used,  2793928
> buff/cache
> KiB Swap:  4194300 total,  4167676 free,    26624 used.  3072468 avail
> Mem
> ...
> > Do you use amd-ucode? Which bootloader do you use?
> grub2-pc (no uEFI) and no amd-ucore yet. If threatened with your life
> for an estimated impact (ballpark figure), what would you say for the
> amd-ucode?
The amd-ucode package only provides the ucode updates from AMD (before
you boot the kernel image).
They are basically firmware enhancements for bugs in the hardware and
are generally recommended.
With grub you won't have to do much to use it (after installing it), but
to update your configuration [1].

Closing, you do mean the package grub when you write grub2-pc, yes?

> > So, you're saying, that you're using two soundcards?
> > That could in theory be a problem (at least to performance).
> Yes, two soundcards, sync'ed amongst each other by SP/DIF, the first
> one clocked/sync'ed from external SP/DIF. Can't do anything about it,
> too many synths. :)
> Not that that's a reason: but it has worked for years, starting with
> 2.6.3x kernels and was easy enough to setup on my first Arch install
> in 2015 or so.
Hm, yes, I guess this shouldn't be a problem. However, ALSA with several
soundcards apparently tends to be unstable for some (with different
soundcards) due to slightly differing clocks and such.

> Haven't felt a need in a long time to tune my system on that level.
> This is good in general and bad for the case in hand. :(
No worries. Usually, there's really not much needed, besides a realtime
kernel and starting jackd with a reasonably high RTPRIO.
I currently use this systemd user unit [2] and these environment configs
[3] (depending on hardware).

Best,
David

[1] https://wiki.archlinux.org/index.php/Microcode#GRUB
[2] https://git.sleepmap.de/dave/dotfiles.git/tree/.config/systemd/user/jack@.service
[3] https://git.sleepmap.de/dave/dotfiles.git/tree/.config/jack

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