There has been a feature on linux (it may still be there to some extent) that if you do a cat /proc/slabinfo and dentry is large that the machine "blips/pauses" some operations.  dentry usually has to be well into the millions (20-100million) to get this behavior, and the pause gets longer the larger the number is.     It is possible that there is some other entry in slabinfo that has similar behavior.  do a cat /proc/slabinfo and see if the output stops for a second, if it does the next entry is the one doing it.

To have this number large you need to have a lot of free ram and be doing a lot of file opens/closes such that the lots of free ram means linux won't reclaim the unused entries and they just accumulate.    On the system I saw it on there was a machine status process doing a cat /proc/slabinfo every minute and it blipped every minute, and it blipped when we manually did the cat /proc/slabinfo.  The solution that was used was to clean up the caches (echo 3  the drop_cache sysinfo I think) weekly and that prevented the issue.  The issue I debugged took weeks to months to build up to the point that that it caused an issue. 

On Fri, Apr 8, 2022 at 6:04 AM Eyal Lebedinsky <fedora@eyal.emu.id.au> wrote:
I am getting back to this issue (see below). I paid attention to sound played with vlc, mythtv and firefox.
I confirmed that I hear the problem with HDMI sound, PC analog audio out socket and an external USB audio device.

The problem is a very short interruption to the sound, not always noticeable but otherwise around 2 seconds after the minute (hh:mm:02).

Just to be sure, I exited thunderbird and firefox, no other GUI applications are running.

I have both pulseaudio and pipewire installed (arrived automatically with dnf update). Is this an issue?
If so then what should be my next step? I am on f34 (probably f36 soon).
- Uninstall both packages and install one only? Which one?
- Or uninstall one and keep the other? Keep which one?

Still, the fact that the disturbance is always on the minute, and all I can find is a cron job that runs at this rate
(logging machine status), can cron be related? Is there something else running every minute in the background on vanilla fedora?
Nothing relevant listed for 'systemctl list-timers'.

TIA

On 01/02/2022 14.43, Eyal Lebedinsky wrote:
> I am on f34 5.15.16-100.fc34.x86_64
>
> This problem started recently (a few weeks, maybe a little longer?).
>
> Initially I noticed audio hiccups when playing mythtv recordings. At times there was also video noise
> but not always.
>
> I then found that playing audio from a network stream (with vlc) also had hiccups. The sound would
> stop and start, sometime even repeat a fraction of a second.
>
> I now played a track from a local disk and the same issues were heard.
>
> There are no messages to indicate a problem. I then used 'mplayer' which has more console messages
> and I now can see an issue:
>
> ==========================================================================
> Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
> libavcodec version 58.134.100 (external)
> Mismatching header version 58.130.100
> AUDIO: 44100 Hz, 2 ch, s16le, 0.0 kbit/0.00% (ratio: 0->176400)
> Selected audio codec: [ffflac] afm: ffmpeg (FFmpeg FLAC audio)
> ==========================================================================
> [AO SDL] Samplerate: 44100Hz Channels: Stereo Format s16le
> AO: [sdl] 44100Hz 2ch s16le (2 bytes per sample)
> Video: no video
> Starting playback...
> A:  49.9 (49.8) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A:  49.9 (49.8) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A:  50.3 (50.3) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A:  50.3 (50.3) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A:  50.4 (50.3) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A:  50.4 (50.3) of 278.4 (04:38.4)  0.6%
> A: 165.7 (02:45.7) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A: 165.7 (02:45.7) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A: 165.8 (02:45.7) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
> A: 165.8 (02:45.7) of 278.4 (04:38.4)  0.6%
> Audio device got stuck!
>
> Here are the sound devices:
>
> $ aplay --list-devices
> **** List of PLAYBACK Hardware Devices ****
> card 0: PCH [HDA Intel PCH], device 0: ALC887-VD Analog [ALC887-VD Analog]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> card 0: PCH [HDA Intel PCH], device 1: ALC887-VD Digital [ALC887-VD Digital]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> card 0: PCH [HDA Intel PCH], device 7: HDMI 1 [HDMI 1]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> card 0: PCH [HDA Intel PCH], device 8: HDMI 2 [HDMI 2]
>    Subdevices: 0/1
>    Subdevice #0: subdevice #0
> card 0: PCH [HDA Intel PCH], device 9: HDMI 3 [HDMI 3]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
> card 0: PCH [HDA Intel PCH], device 10: HDMI 4 [HDMI 4]
>    Subdevices: 1/1
>    Subdevice #0: subdevice #0
>
> I get similar problems with [HDMI 3] and with [ALC887-VD Analog] selected using pavucontrol.
>
> lspci shows
>      Audio device: Intel Corporation Cannon Lake PCH cAVS (rev 10)
>
> What can I do now to diagnose the problem?
>
> One more data point: for a long time (many months) I had a problem where the system locks up hard
> needing a cold restart. There were no hiccups otherwise. It always had mythtv playing or YouTube.
> When locked the sound of the last second would loop continuously until the reset. The video is frozen then.
> Maybe related? This is a long running problem (happens once every few months) but the audio stutter
> is a recent, new issue.
>
> TIA
>

--
Eyal Lebedinsky (fedora@eyal.emu.id.au)
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