[vfio-users] Why does the audio from VM crackle?
Ivan Volosyuk
ivan.volosyuk at gmail.com
Tue Jun 14 08:05:42 UTC 2016
I struggled with the rare (but very annoying) crackles and finally I don't
have them anymore with emulated audio.
I use cpu isolation and keep 2 CPU threads for host out of 8.
I use MSI as per alex's VFIO blog.
I pass following env to qemu:
QEMU_AUDIO_DRV=pa
QEMU_PA_SAMPLES=1024
PULSE_COOKIE=/home/ivan/.config/pulse/cookie
PULSE_SERVER=unix:/home/ivan/.pulse_server
I switched qemu to -soundhw ac97
I have hv_time in cpu string:
host,kvm=off,hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time,hv-vendor-id=servo,hv-vpindex,hv-reset,hv-runtime,hv-crash
I have following rtc settings: -rtc base=utc,driftfix=slew -no-hpet -global
kvm-pit.lost_tick_policy=discard
# cd .pulse; grep -r ivan .
./default.pa:load-module module-native-protocol-unix srbchannel=1
socket=/home/ivan/.pulse_server
./client.conf:default-server = unix:/home/ivan/.pulse_server
pulse/daemon.conf:
realtime-scheduling = yes
# values which seem to work for me
default-fragments = 2
default-fragment-size-msec = 125
enable-shm = yes
shm-size-bytes = 0
realtime-priority = 5
On Fri, Jun 10, 2016 at 6:15 AM Abdulla Bubshait <abdulla.bubshait at gmail.com>
wrote:
> The CPU isolation and interrupt reduction for the guest CPUs seems to
> have greatly reduced the audio problems.
>
> Thanks for that.
>
> On Thu, Jun 9, 2016 at 12:43 PM, Milos Kaurin <milos.kaurin at gmail.com>
> wrote:
> > Yes, this keeps coming up now and again on this list.
> >
> > My solution was:
> >
> > 1. Buy a dedicated PCIE sound card
> > 2. Pass it through to the guest
> > 3. Route audio: mobo soundcard > guest soundcard
> >
> > In essence, the always-on guest would handle audio, but I would still
> have
> > crackles (rarely), especially from the web browsers (host & guest). Games
> > not so much.
> >
> > To fix crackles, I did the following:
> > 1. In the kernel cmdline: Use hugepages, 16x1GB for the guest (16 for the
> > host, 32 total)
> > 2. In the kernel cmdline: Use cpuisol (6 cores for the gues, 2 for the
> host)
> > 3. In the kernel cmdline: Use nohz_full and rcu_nocbs for the guest cores
> > 4. In the virt XML: Use cputune, hugepages, cpu mode=host-passthrough
> with
> > the correct topology
> > 5. In the virt XML: iothreadpin and emulatorpin for the 2 host CPUs
> > 6. In the virt XML: Use virtio wherever possible (net, block devices)
> >
> > I think I covered everything. If anyone else has any other tips, please
> let
> > me know.
> >
> >
> >
> > Appenix
> >
> >
> > My /etc/default/grub:
> >
> > GRUB_CMDLINE_LINUX="rhgb quiet intel_iommu=on iommu=pt kvm.ignore_msrs=1
> > rd.driver.pre=vfio-pci hugepagesz=1G default_hugepagesz=1G hugepages=16
> > nohz_full=1,2,3,5,6,7 rcu_nocbs=1,2,3,5,6,7 isolcpus=1,2,3,5,6,7"
> >
> >
> >
> > My XML:
> >
> > <domain type='kvm'>
> > <name>Win10</name>
> > <uuid>4bb72e5b-c886-425f-8280-b69755ebf054</uuid>
> > <memory unit='KiB'>16777216</memory>
> > <currentMemory unit='KiB'>16777216</currentMemory>
> > <memoryBacking>
> > <hugepages/>
> > </memoryBacking>
> > <vcpu placement='static'>6</vcpu>
> > <iothreads>2</iothreads>
> > <cputune>
> > <vcpupin vcpu='0' cpuset='1'/>
> > <vcpupin vcpu='1' cpuset='5'/>
> > <vcpupin vcpu='2' cpuset='2'/>
> > <vcpupin vcpu='3' cpuset='6'/>
> > <vcpupin vcpu='4' cpuset='3'/>
> > <vcpupin vcpu='5' cpuset='7'/>
> > <emulatorpin cpuset='0,4'/>
> > <iothreadpin iothread='1' cpuset='0'/>
> > <iothreadpin iothread='2' cpuset='4'/>
> > </cputune>
> > <os>
> > <type arch='x86_64' machine='pc-i440fx-2.4'>hvm</type>
> > <loader readonly='yes'
> > type='pflash'>/usr/share/edk2.git/ovmf-x64/OVMF_CODE-pure-efi.fd</loader>
> > <nvram>/var/lib/libvirt/qemu/nvram/Win10_VARS.fd</nvram>
> > </os>
> > <features>
> > <acpi/>
> > <apic/>
> > <kvm>
> > <hidden state='on'/>
> > </kvm>
> > <vmport state='off'/>
> > </features>
> > <cpu mode='host-passthrough'>
> > <topology sockets='1' cores='3' threads='2'/>
> > </cpu>
> > <clock offset='localtime'>
> > <timer name='rtc' tickpolicy='catchup'/>
> > <timer name='pit' tickpolicy='delay'/>
> > <timer name='hpet' present='no'/>
> > </clock>
> > <on_poweroff>destroy</on_poweroff>
> > <on_reboot>restart</on_reboot>
> > <on_crash>restart</on_crash>
> > <pm>
> > <suspend-to-mem enabled='no'/>
> > <suspend-to-disk enabled='no'/>
> > </pm>
> > <devices>
> > <emulator>/usr/bin/qemu-kvm</emulator>
> > <disk type='block' device='disk'>
> > <driver name='qemu' type='raw' cache='none' io='native'/>
> > <source dev='/dev/sdb'/>
> > <target dev='vda' bus='virtio'/>
> > <boot order='2'/>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x09'
> > function='0x0'/>
> > </disk>
> > <controller type='pci' index='0' model='pci-root'/>
> > <controller type='scsi' index='0' model='virtio-scsi'>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
> > function='0x0'/>
> > </controller>
> > <controller type='usb' index='0' model='none'/>
> > <interface type='bridge'>
> > <mac address='52:54:00:3e:c8:03'/>
> > <source bridge='br0'/>
> > <model type='virtio'/>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x03'
> > function='0x0'/>
> > </interface>
> > <hostdev mode='subsystem' type='pci' managed='yes'>
> > <source>
> > <address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
> > </source>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x0a'
> > function='0x0'/>
> > </hostdev>
> > <hostdev mode='subsystem' type='pci' managed='yes'>
> > <source>
> > <address domain='0x0000' bus='0x01' slot='0x00' function='0x1'/>
> > </source>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x0b'
> > function='0x0'/>
> > </hostdev>
> > <hostdev mode='subsystem' type='pci' managed='yes'>
> > <source>
> > <address domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
> > </source>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x02'
> > function='0x0'/>
> > </hostdev>
> > <hostdev mode='subsystem' type='pci' managed='yes'>
> > <source>
> > <address domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
> > </source>
> > <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
> > function='0x0'/>
> > </hostdev>
> > <memballoon model='none'/>
> > </devices>
> > </domain>
> >
> >
> >
>
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