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

[Janusz]

W dniu 09.06.2016 o 18:52, Abdulla Bubshait pisze:
> On Thu, Jun 9, 2016 at 10:55 AM, Alex Williamson
> <alex.l.williamson at gmail.com> wrote:
>> This seems rather obvious doesn't it?  An emulated audio device is just a
>> blob of code that requires the CPU to run it.  Generating audio, it's highly
>> susceptible to latency issues.  At the same time you're apparently playing a
>> game that consumes significant CPU time.  Total CPU cycles on the system
>> have a fixed limit.  Therefore any time you exceed that limit or get close
>> enough for scheduling latency to become an issue, you can expect the audio
>> emulation to suffer.  This is why bare metal has devices dedicated to
>> various activities.  Solutions are 1) get a faster system, 2) load the
>> system less or maybe more optimally, 3) assign a device to offload the work.
>>
>> The "more optimally" part of 2) might include pinning vCPUs, pinning the
>> emulator thread, leaving sufficient CPU power unassigned so that the host
>> has enough capacity to run emulation at full speed, reducing host overhead
>> via things like hugepages, etc...
> I don't need to be playing games for it to have problems. I shut down
> everything in
> both the host and guest, plenty of cycles to spare. If I were to test
> the speaker setting
> in the windows Control Panel I get crackling. I have an i7 4790 so I
> thought I had
> enough cycles to be able to handle that part on its own.
>
> I do have vCPUs pinned to 2 of the cores, leaving 2 cores for the
> host. I also have
> hugepages setup. I tried changing the governor to performance and pinning qemu
> to non-VM cores. It seems I cannot get a setup that doesn't have audio issues.
>
> I was wondering if there was a better way to move audio from the guest
> to the host.
>
Make sure you disable any input devices and other output devices you are
not using in windows (like hdmi audio). Also, are you running with
-nographic option? if no, then try with it. I had those problems, but
this helped me fix them.