Re: audio problem

[Roger Heflin]

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(a)eyal.emu.id.au&gt;
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(a)eyal.emu.id.au)
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