high IO-Delay and IO Pressure Stall with 0.24

[lucker999]

Bug report

Describe the bug

I would like to report similar symptoms on Debian-based system (Proxmox VE) as per the issue #2241

• OS/Environment: Proxmox VE (Debian-based), music_directory on ZFS pool (HDD mirror + NVMe special vdev), exported via NFS (sharenfs with async added, nohide, anonuid=1001, anongid=1001, all_squash, rw=172.22.11.0/24). MPD runs as user service (systemctl --user), output to PulseAudio (PipeWire backend) → local Roland USB DAC.
• Symptoms:
  • Constant high IO pressure/stall: 50% IO delay, 85-95% pressure (from zpool iostat / pressure stall metrics) right after MPD starts.
  • Flat/constant (minor fluctuations), not spikes during scans/playback.
  • Stopping MPD (systemctl --user stop mpd) immediately drops IO to near-zero.
  • Restarting MPD reproduces the issue instantly, even with no clients connected (Cantata/M.A.L.P./ncmpcpp closed).
  • iotop -o shows nfsd as the top reader (e.g., 100-200 MB/s bursts, then steady lower reads), despite local playback only—no network streaming.
  • ARC stats excellent (demand metadata hits 100%, overall ~99.9%), so not metadata thrashing.
  • Tried mitigations (all ineffective):
    • Commented out sticker_file (disabled stickers DB).
    • Added auto_update "no" (explicitly disable auto DB updates).
    • Added async to NFS share for music dir (though mpd access the music dir directly).
    • atime=off recursively on pool (already done earlier).
• Workarounds tested:
  • Downgrade to 0.23.x not possible (Debian trixie only has 0.24.4; no older in repos).
  • No disk thrashing visible in zpool iostat -v 1 during idle (activity mostly on main HDD mirror via nfsd).

Expected Behavior

No IO delay or/and IO pressure stall while mpd is running.

Actual Behavior

Version

MPD version: 0.24.4-1 (from Debian trixie repo)
Music Player Daemon 0.24.4 (0.24.4)
Copyright 2003-2007 Warren Dukes warren.dukes@gmail.com
Copyright 2008-2025 Max Kellermann max.kellermann@gmail.com
This is free software; see the source for copying conditions. There is NO
warranty; not even MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Database plugins:
simple proxy upnp

Storage plugins:
local smbclient udisks nfs curl

Neighbor plugins:
smbclient upnp udisks

Decoder plugins:
[mpg123] mp3
[mad] mp3 mp2
[vorbis] ogg oga
[oggflac] ogg oga
[flac] flac
[opus] opus ogg oga
[dsdiff] dff
[dsf] dsf
[faad] aac
[mpcdec] mpc
[wavpack] wv
[openmpt] mptm mod s3m xm it 669 amf ams c67 dbm digi dmf dsm dtm far imf ice j2b m15 mdl med mms mt2 mtm nst okt plm psm pt36 ptm sfx sfx2 st26 stk stm stp ult wow gdm mo3 oxm umx xpk ppm mmcmp
[modplug] 669 amf ams dbm dfm dsm far it med mdl mod mtm mt2 okt s3m stm ult umx xm
[mikmod] amf dsm far gdm imf it med mod mtm s3m stm stx ult uni xm
[sidplay] sid mus str prg P00
[wildmidi] mid
[fluidsynth] mid
[adplug] amd d00 hsc laa rad raw sa2
[gme] ay gbs gym hes kss nsf nsfe rsn sap spc vgm vgz
[ffmpeg] 264 265 266 302 3g2 3gp 4xm 669 722 aa aa3 aac aax ac3 ac4 ace acm act adf adp ads adx aea afc aiff aix al alias_pix alp amf amr amrnb amrwb ams anm ans apc ape apl apm apng aptx aptxhd aqt argo_asf argo_brp argo_cvg art asc asf asf_o ass ast au avc avi avif avr avs avs2 avs3 bcstm bethsoftvid bfi bfstm bin bink binka bit bitpacked bmp_pipe bmv boa bonk brender_pix brstm c2 c93 caf cdata cdg cdxl cgi cif cine codec2raw concat cri_pipe dash dat data daud dav dbm dds_pipe dfa dff dfpwm dif digi dirac diz dmf dnxhd dpx_pipe dsf dsicin dsm dss dst dtk dtm dts dtshd dv dvbsub dvbtxt dvdvideo dxa ea eac3 ec3 evc exr_pipe f32be f32le f4v f64be f64le fap far ffmetadata film_cpk fits flac flic flm flv frm fsb fwse g722 g723_1 g726 g726le g729 gdm gdv gem_pipe genh gif gif_pipe gsm gxf h261 h263 h264 h265 h266 h26l hca hcom hdr_pipe heic heif hevc hls hnm iamf ice ico idcin idf idx iff ifv ilbc image2 image2pipe imf imx ipmovie ipu ircam ism isma ismv iss it iv8 ivf ivr j2b j2k j2k_pipe jacosub jpeg_pipe jpegls_pipe jpegxl_pipe jv jxl kux kvag laf lc3 libgme lmlm4 loas lrc lvf lxf m15 m2a m4a m4b m4v mac mca mcc mdl med mgsts microdvd mj2 mjpeg mjpg mk3d mka mks mkv mlp mlv mm mmcmp mmf mms mo3 mod mods moflex mov mp2 mp3 mp4 mpa mpc mpc8 mpeg mpegts mpegtsraw mpegvideo mpl2 mpo mptm msbc msf msnwctcp msp mt2 mtaf mtm mtv musx mv mvi mxf mxg nfo nist nsp nst nsv nut nuv obu ogg okt oma omg osq paf pam_pipe pbm_pipe pcx_pipe pdv pfm_pipe pgm_pipe pgmyuv_pipe pgx_pipe phm_pipe photocd_pipe pictor_pipe pjs plm pmp png_pipe pp_bnk ppm ppm_pipe psd_pipe psm psp psxstr pt36 ptm pva pvf qcif qcp qdraw_pipe qoa qoi_pipe r3d rco rcv rcwt rgb rka rl2 rm roq rpl rsd rso rt rtp rtsp s16be s24be s24le s32be s32le s337m s3m sami sap sb sbc sbg scc scd sdns sdp sdr2 sds sdx ser sf sfx sfx2 sga sgi_pipe shn sln smi smk smush sol son sox spdif sph srt ss2 st26 stk stl stm stp str sub sunrast_pipe sup svag svg_pipe svs sw swf tak tco tedcaptions thd thp tiertexseq tiff_pipe tmv tta txd txt ty ty+ u16be u24be u24le u32be u32le ub ul ult umx usm uw v v210 vag vb vbn_pipe vc1 vidc viv vividas vmd voc vpk vqe vqf vql vt vtt vvc w64 wa wav way wc3movie webm webm_dash_manifest webp_pipe wma wow wsaud wsd wsvqa wtv wv wve xa xbin xbm_pipe xl xm xmd xmv xpk xpm_pipe xvag xwd_pipe xwma y4m yop yuv yuv10 rtp:// rtsp:// rtsps://
[sndfile] wav aiff aif au snd paf iff svx sf voc w64 pvf xi htk caf sd2
[pcm]

Filters:
libsamplerate soxr

Tag plugins:
id3tag

Output plugins:
shout null fifo sndio pipe alsa ao oss openal pipewire pulse jack httpd snapcast recorder

Encoder plugins:
null vorbis opus lame wave flac

Archive plugins:
[bz2] bz2
[zzip] zip
[iso] iso

Input plugins:
file io_uring archive alsa curl ffmpeg smbclient nfs mms cdio_paranoia

Playlist plugins:
extm3u m3u pls xspf asx rss flac cue embcue

Protocols:
file:// alsa:// cdda:// ftp:// ftps:// gopher:// hls+http:// hls+https:// http:// https:// mms:// mmsh:// mmst:// mmsu:// nfs:// rtmp:// rtmpe:// rtmps:// rtmpt:// rtmpte:// rtmpts:// rtp:// rtsp:// rtsps:// scp:// sftp:// smb:// srtp://

Other features:
avahi dbus udisks epoll icu inotify ipv6 systemd tcp un

Configuration

music_directory "/zd/md/media/music"
playlist_directory "/.config/mpd/playlists"
db_file "/.config/mpd/tag_cache"
state_file "/.config/mpd/state"
# sticker_file "/.config/mpd/sticker.sql"
# If you use systemd, do not configure a log_file. With systemd, MPD
# defaults to the systemd journal, which is fine.
log_file "~/.config/mpd/mpd.log"
log_level "verbose"
user "jukebox"
bind_to_address "0.0.0.0"
port "6600"
auto_update "no"
restore_paused "yes"
save_absolute_paths_in_playlists "yes"
audio_output {
type "pulse"
name "Roland QUAD-CAPTURE"
server "/run/user/1001/pulse/native"
sink "alsa_output.usb-Roland_QUAD-CAPTURE_0000EA03AB0FAC3E72118D2B1B1260F0-00.analog-surround-40"
}
filesystem_charset "UTF-8"

Log

Nothing useful in logs; the minor things:
output: OutputThread could not get realtime scheduling, continuing anyway: sched_setscheduler failed: Operation not permitted
event: RTIOThread could not get realtime scheduling, continuing anyway: sched_setscheduler failed: Operation not permitted

[MaxKellermann]

Your MPD version is too old and unsupported.

Your issue is really a Linux kernel bug and has been reported several times (#2241). There is a workaround (#2412) but your Debian version can't use that workaround because its liburing version is too old. And of course, your MPD version is outdated and doesn't have the workaround.

Please never report problems with outdated MPD versions. Not even if it's the latest packaged version in the distribution of your choice. This project does not support Debian "stable".