https://git.qemu.org/?p=qemu.git;a=commitdiff;h=6cdc2d189cb60a9d13e
** Changed in: qemu
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1795527
Title:
Malformed audio and video output stuttering after upgrade to QEMU 3.0
Status in QEMU:
Fix Released
Bug description:
My host is an x86_64 Arch Linux OS with a recompiled 4.18.10 hardened
kernel, running a few KVM guests with varying OSes and configurations
managed through a Libvirt stack.
Among these guests I have two Windows 10 VMs with VGA passthrough and
PulseAudio-backed virtual audio devices.
After upgrading to QEMU 3.0.0, both of the Win10 guests started
showing corrupted audio output in the form of unnatural reproduction
speed and occasional but consistently misplaced audio fragments
originating from what seems to be a circular buffer wrapping over
itself (misbehaviour detected by starting some games with known OSTs
and dialogues: soundtracks sound accelerated and past dialogue lines
start replaying middle-sentence until the next line starts playing).
In addition, the video output of the malfunctioning VMs regularly
stutters roughly twice a second for a fraction of a second (sync'ed
with the suspected buffer wrapping and especially pronounced during
not-pre-rendered cutscenes), toghether with mouse freezes that look
like actual input misses more than simple lack of screen refreshes.
The issue was succesfully reproduced without the managing stack, directly
with the following command line, on the most capable Windows guest:
QEMU_AUDIO_DRV=pa
QEMU_PA_SERVER=127.0.0.1
/usr/bin/qemu-system-x86_64 -name guest=win10_gms,debug-threads=on \
-machine pc-i440fx-3.0,accel=kvm,usb=off,vmport=off,dump-guest-core=off \
-cpu
host,hv_time,hv_relaxed,hv_vapic,hv_spinlocks=0x1fff,hv_vendor_id=123456789abc,kvm=off
\
-drive
file=/usr/share/ovmf/x64/OVMF_CODE.fd,if=pflash,format=raw,unit=0,readonly=on \
-drive
file=/var/lib/libvirt/qemu/nvram/win10_gms_VARS.fd,if=pflash,format=raw,unit=1 \
-m 5120 \
-realtime mlock=off \
-smp 3,sockets=1,cores=3,threads=1 \
-uuid 39b56ee2-6bae-4009-9108-7be26d5d63ac \
-display none \
-no-user-config \
-nodefaults \
-rtc base=localtime,driftfix=slew \
-global kvm-pit.lost_tick_policy=delay \
-no-hpet \
-no-shutdown \
-global PIIX4_PM.disable_s3=1 \
-global PIIX4_PM.disable_s4=1 \
-boot strict=on \
-device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x4.0x7 \
-device
ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x4 \
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x4.0x1 \
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x4.0x2 \
-device ahci,id=sata0,bus=pci.0,addr=0x9 \
-drive
file=/dev/vms/win10_gaming,format=raw,if=none,id=drive-virtio-disk0,cache=none,aio=native
\
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,write-cache=on
\
-drive
file=/dev/sr0,format=raw,if=none,id=drive-sata0-0-0,media=cdrom,readonly=on \
-device ide-cd,bus=sata0.0,drive=drive-sata0-0-0,id=sata0-0-0 \
-device intel-hda,id=sound0,bus=pci.0,addr=0x3 \
-device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 \
-device usb-host,hostbus=2,hostaddr=3,id=hostdev0,bus=usb.0,port=1 \
-device vfio-pci,host=01:00.0,id=hostdev1,bus=pci.0,addr=0x6 \
-device vfio-pci,host=01:00.1,id=hostdev2,bus=pci.0,addr=0x7 \
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8 \
-sandbox
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
-msg timestamp=on
By "purposedly misconfiguring" the codepaths and replacing "pc-i440fx-3.0"
with "pc-i440fx-2.11" (basically reverting the config changes I needed to do in
order to update the domain definitions), the stuttering seems to disappear (or
at least becomes negligible) and the audio output, despite becoming incredibly
distorted, is consistent in every other way, with in-order dialogues and
(perceived) correct tempo.
In order to exclude eventual misconfigurations in the host's audio processing
pipeline, I proceeded to update the domain definition's codepath of another
guest running Ubuntu 18.04 with a completely different hardware configuration
(no video card passthrough and no PulseAudio backconnection, just a plain
emulated VirtIO display and Spice audio device).
The audio issue presented itself again in the form of slightly sped up audio
playback from Internet videos interleaved with occasional "quenches" of playing
speed.
Stutters are difficult to detect because of the poor refresh rate of the
emulated VGA adapter, but I wouldn't be surprised to find them here too
(actually, I *think* I sensed them, but I'm not sure enough to assess their
existence).
Once again, by reverting to the old 2.11 directive everything is back
to normal.
Given the fact that no official upgrade directives regarding required
sampling rate, period or sheduling adjustments were stated or handed-out to
administrators, I decided to report this behaviour as a bug.
I hope this is the appropriate channel and that I didn't annoy anyone (this
is my first proper bug report, please forgive me for any innaccuracy).
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