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Re: [vfio-users] Why does the audio from VM crackle?



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 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 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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