How can I eliminate xruns when I use jackminimix?

[crocket]

Raspberry Pi 3 B+:

jackd -P 90 -d alsa -d speakers -p 384 -n 2 -r 48000

(384 = 48 frames/ms * 8 ms = 128 frames/period * 3 periods/buffer)

jack_netsource -n 3 -H my_desktop_computer

My Desktop Computer:

jack -P 90 -d netone -n 3
zita-a2j -j spdifin -d spdifin -p 128 -n 3 -r 48000

(spdif-in of a USB soundcard is connected to spdif-out of my onboard soundcard. Default alsa PCM device is ALSA dmix which outputs to spdif-out of my onboard soundcard.)

zita-j2a -j headphones -d headphones -p 128 -n 3 -r 48000
jackminimix -c -p port -n spk-vol
jackminimix -c -p port -n hdp-vol

Connections managed by my own jack connection manager that I wrote in python:

Speaker mode:

Display in i3 bar

Headphone mode:

Display in i3 bar

Xruns from netone while CPU load is close to 100%:

JackEngine::XRun: client = spdifin was not finished, state = Running
JackEngine::XRun: client = headphones was not finished, state = Running
JackEngine::XRun: client hdp-vol finished after current callback
JackEngine::XRun: client = spk-vol was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error

Possibilities:

1. Either, spdifin or headphones couldn't finish in time.
2. Either, hdp-vol or spk-vol didn't finish in time.
3. hdp-vol finished after current callback means hdp-vol didn't finish time and caused xruns in other JACK clients.

Question:

What caused xruns?

[crocket]

I guess xruns were caused because

1. /etc/cgroup/cgrules.conf didn't assign jackminimix to audio cgroup which allocates 95% of CPU time to realtime threads of its cgroup members.
2. jackd was started before cgrulesengd started working. Thus, cgrulesengd couldn't assign jackd to audio group.

I added jackminimix to audio cgroup in /etc/cgroup/cgrules.conf and made sure that jackd starts after cgrulesengd starts.

audio cgroup includes jackd, zita-a2j, zita-j2a, and jackminimix.

[crocket]

After fixing cgroup issue, I still get xruns.

Xruns seems to come from spk-vol in headphone mode and hdp-vol in speaker mode.

So, I severed connections between hdp-vol and headphones in speaker mode and spk-vol and system in headphone mode.

But, severing unused connections doesn't remove xruns.

hdp-vol finishes after a callback in speaker mode, and spk-vol finishes after a callback in headphone mode.

[crocket]

Executing stress-ng --iomix 8 --ionice-class idle reliably causes xruns.

[crocket]

My CPU is FX-8300 which has 4 cores and 8 threads.

nice -n 19 stress-ng --iomix 8 --ionice-class idle -t 5m caused multiple xruns.

nice -n 19 stress-ng --cpu 8 -t 5m didn't cause xruns.

I tried giving realtime ionice priorities to jackd and all JACK clients, but stress-ng --iomix 8 still managed to cause xruns.

I tweaked realtime ionice priorities, frames per periods, and periods per buffer. The following setup seems to withstand

nice -n 19 stress-ng --iomix 8 --ionice-class idle --cpu 8 -t 5m

without xruns.

On Raspberry Pi 3 B+:

ionice -c 1 -n 0 sudo -u pi jackd -P 90 -d alsa -d speakers -p 256 -n 2 -P -r 48000
ionice -c 1 -n 2 sudo -u pi jack_netsource -H my_desktop_computer -n 3 -m 1500

On my desktop computer:

Programs started in init scripts

ionice -c 1 -n 2 sudo -u user jackd -P 90 -d netone -n 3
ionice -c 1 -n 0 sudo -u user stdbuf -o 0 zita-a2j -j from_alsa -d spdif_in -p 128 -n 3 -r 48000
ionice -c 1 -n 0 sudo -u user stdbuf -o 0 zita-j2a -j headphones -d xfihd_hdp -p 128 -n 3 -r 48000
ionice -c 1 -n 4 sudo -u user stdbuf -o 0 jackminimix -c 2 -p 20255 -n soft-vol

~/.asoundrc

defaults.pcm.rate_converter "samplerate_best"

pcm.spdif_out {
  type hw
  card SB
  device 1
  subdevice 0
  format S16_LE
  rate 48000
  channels 2
}

pcm.smix {
  type dmix
  ipc_key 219348
  hw_ptr_alignment "rounddown"
  slave {
    pcm "spdif_out"
    period_size 512
    periods 3
    format S16_LE
    rate 48000
    channels 2
  }
  bindings {
    0 0
    1 1
  }
}

pcm.spdif_in {
  type hw
  card HD
  device 1
  subdevice 0
  format S16_LE
  rate 48000
  channels 2
}

pcm.xfihd_hdp {
  type hw
  card HD
  device 0
  subdevice 0
  format S16_LE
  rate 48000
  channels 2
}

ctl.xfihd_hdp {
  type hw
  card HD
}

pcm.!default {
  type plug
  slave.pcm {
    @func getenv
    vars [ MY_ALSA_DEVICE ]
    default "smix"
  }
  rate_converter "samplerate_best"
}

Conclusion

I guess that writing to ZFS interferes with reading from and writing to USB soundcard or ethernet adaptor. I thought ionice only affected file system operations.

Perhaps, does ionice affect xruns because I log stdout and stderr of jackd, zita-ajbridge, and jackminimix into files on ZFS without buffering? ( stdbuf -o 0 removes buffering. )

I will report this issue to jack2.