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



On Thu, Jun 9, 2016 at 10:55 AM, Alex Williamson
<alex l williamson 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.


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