Audio "Stuttering"

Today I’ve started having problems with audio playback stuttering. The current session has only 5 MIDI tracks and the DSP is shown to be under 50%. The plugins are Drumgizmo, u-he Diva, zynaddsubfx, MODO Bass, and Hammond B-3X. (The last two running under wine with yabridge.) The session had sample rate of 48kHz, buffer size of 2048, and 3 periods (the same as usual for me when mixing or programming MIDI). I am using ALSA and not Jack.

I did not have this problem at all earlier this week. Since I had just installed (today) version 7.4, I thought that that could be the problem, but reverting to 7.3 did not fix it.

I did not have any problems before with a non-RT kernel (which failed the sanity check), but even with the RT kernel, the problem persists.

I’ve run with gdb, but I don’t see anything relevant:

Here is some info about the system (basically running Debian Sid with Debian’s RT kernel):

$ inxi -v3
  Host: debian Kernel: 6.1.0-8-rt-amd64 arch: x86_64 bits: 64 compiler: gcc
    v: 12.2.0 Desktop: KDE Plasma v: 5.27.2 Distro: aptosid 2013-01 - kde-full
    - (201305050307) base: Debian GNU/Linux 12 (bookworm)
  Type: Desktop System: ASUS product: All Series v: N/A
    serial: <superuser required>
  Mobo: ASUSTeK model: Z87-PRO v: Rev 1.xx serial: <superuser required>
    UEFI: American Megatrends v: 2103 date: 08/18/2014
  Device-1: hidpp_battery_0 model: Logitech M310
    charge: 55% (should be ignored) status: discharging
  Device-2: wacom_battery_0 model: Wacom Intuos S charge: 0% status: N/A
  Info: quad core model: Intel Core i7-4771 bits: 64 type: MT MCP
    arch: Haswell rev: 3 cache: L1: 256 KiB L2: 1024 KiB L3: 8 MiB
  Speed (MHz): avg: 3849 high: 3900 min/max: 800/3900 cores: 1: 3498 2: 3900
    3: 3900 4: 3900 5: 3900 6: 3900 7: 3900 8: 3900 bogomips: 55966
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
  Device-1: AMD Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
    vendor: VISIONTEK driver: amdgpu v: kernel arch: GCN-1 bus-ID: 01:00.0
    temp: 51.0 C
  Device-2: Logitech Webcam C270 type: USB driver: snd-usb-audio,uvcvideo
    bus-ID: 3-3.3:8
  Display: x11 server: X.Org v: with: Xwayland v: 22.1.9 driver: X:
    loaded: amdgpu dri: radeonsi gpu: amdgpu resolution: 1: 1920x1080~60Hz
    2: 1920x1080~60Hz
  API: OpenGL v: 4.6 Mesa 22.3.6 renderer: AMD Radeon Graphics (verde LLVM
    15.0.6 DRM 3.49 6.1.0-8-rt-amd64) direct-render: Yes
  Device-1: Intel Ethernet I217-V vendor: ASUSTeK driver: e1000e v: kernel
    port: f040 bus-ID: 00:19.0
  IF: eth0 state: up speed: 100 Mbps duplex: full mac: e0:3f:49:a3:4c:a6
  Local Storage: total: 13.88 TiB used: 7.17 TiB (51.7%)
  Processes: 375 Uptime: 28m Memory: 31.28 GiB used: 5.27 GiB (16.9%)
  Init: systemd target: graphical (5) Compilers: gcc: 12.2.0 Packages: 7469
  Shell: Bash v: 5.2.15 inxi: 3.3.26
$ inxi -A
  Device-1: Intel 8 Series/C220 Series High Definition Audio driver: N/A
  Device-2: AMD Oland/Hainan/Cape Verde/Pitcairn HDMI Audio [Radeon HD 7000
    Series] driver: N/A
  Device-3: Focusrite-Novation Focusrite Scarlett 2i2 2nd Gen type: USB
    driver: snd-usb-audio
  Device-4: Logitech Webcam C270 type: USB driver: snd-usb-audio,uvcvideo
  API: ALSA v: k6.1.0-8-rt-amd64 status: kernel-api
  Server-1: PulseAudio v: 16.1 status: active

Any ideas what the problem might be?

Some more info: when having the stuttering problem, pressing the space bar while playing does not stop, but restart playing. (With Auto Return enabled, it returns to the position and plays again.) To stop I had to click on the Stop button.

I tried running the same project with Jack instead of ALSA, and I do not get the stuttering and playing the audio works fine, but when I stop playing I get a “machine gun” effect and the xrun counts jumps by about 10 every time.

Here is the result of rtcqs:

$ rtcqs
rtcqs - version 0.5.3

Root User
[ OK ] Not running as root.

Audio Group
[ OK ] User finotti is in the audio group.

CPU Frequency Scaling
[ OK ] The scaling governor of all CPU's is set at performance.

Kernel Configuration
[ OK ] Valid kernel configuration found.

High Resolution Timers
[ OK ] High resolution timers are enabled.

Tickless Kernel
[ WARNING ] Tickless timer support is not not set. Try enabling tickless timer support (CONFIG_NO_HZ_IDLE, or CONFIG_NO_HZ in older kernels). See also

Preempt RT
[ OK ] Kernel 6.1.0-8-rt-amd64 is using threaded IRQ's.

Spectre/Meltdown Mitigations
[ WARNING ] Kernel with Spectre/Meltdown mitigations found. This could have a negative impact on the performance of your system. See also

RT Priorities
[ OK ] Realtime priorities can be set.

[ OK ] Swappiness is set at 10.

[ OK ] The following mounts can be used for audio purposes: /, /gnu/store, /media/music, /media/data2, /media/data3, /media/media, /media/sg4tb, /media/sd_data
[ WARNING ] The following mounts should be avoided for audio purposes: /run/user/1000/doc. See also

[ OK ] USB port ehci_hcd:usb1 with IRQ 16 does not share its IRQ.
USB port ehci_hcd:usb2 with IRQ 23 does not share its IRQ.
USB port xhci_hcd with IRQ 29 does not share its IRQ.

Power Management
[ OK ] Power management can be controlled from user space. This enables DAW's like Ardour and Reaper to set CPU DMA latency which could help prevent xruns.

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