[vfio-users] I need your help!

Thu Feb 23 12:02:32 UTC 2017

Hi Paige

I noticed your -cpu option does not disable hypervisor; you might want
to try it, please see
http://vfio.blogspot.co.uk/2016/10/how-to-improve-performance-in-windows-7.html
for reference. On the example of my virtual machines, this translates to
qemu options:

-machine pc-i440fx-2.5,accel=kvm,usb=off,dump-guest-core=off,mem-
merge=off -cpu host,-
hypervisor,hv_time,hv_relaxed,hv_vapic,hv_spinlocks=0x1000

Another thing, I make use of vCPU pinning in my libvirt configuration
and I think this would help you as well. The CPUs I use for virtual
machines are removed from Linux kernel scheduler, with "isolcpus"
option. FWIW my motherboard is SuperMicro X9DA7. And one more thing,
when setting up my VMs I took particular care to ensure that the
physical cores I pinned my vCPUs to, are all on the same socket and
directly attached to PCIe slots that I mapped to my VMs with vfio.

B.

--

  Bronek Kozicki

  brok at spamcop.net

On Thu, 23 Feb 2017, at 11:22 AM, Paige Thompson wrote:

> I have been running this setup since October and I have tried since
> this time to fix the same issues without any success either in terms
> of isolating the problem or fixing it. Here’s a lot of details/specs
> about the setup that I could think of off-hand to include:
>  

> https://gist.github.com/cloudkitsch/eefec59233269ace0c9707d0a57e0d5f
>  

> However before diving into that I want to merely point out that the
> problem I’m having is not specific to my graphics configuration which
> works just fine except that HDMI audio doesn’t work. Not really sure
> why, maybe because I’m running Windows 10 N? Don’t know. Seems like I
> remember HDMI audio working on my Radeon 5770 / Opteron setup that I
> had VFIO setup on quite a while ago.
>  

> I don’t really want HDMI audio either. I have a Yamaha MG10-XU mixer
> connected to a USB 3 PCIe card that is also passed through to the
> guest. It is a USB audio DAC. The problem I’m having is very
> specifically with this mixer however the mixer works just fine on
> other computers. It doesn’t matter what buffer size I’m using @
> 44.1khz (lowest sampling rate) I still have the same problem which is
> hard to explain because while I can reproduce it consistently I can’t
> understand the behavior. Asides from theories, I’m not really sure
> where I would start to test. I think that other people around me are
> more frustrated with it than I am but I would really like to first
> isolate the problem and provide my time (while available) to do what I
> can to eliminate the behavior or fix the problem.
>  

> I would like to suggest a few reasons why it might be happening,
> starting with the fact that the audio will start to skip when the load
> on the bare metal host increases or is saturated. This is not always
> the case, but I have not found a way to dedicate specific cores to the
> gust without having to do something really backwards with numactl to
> ensure nothing ever touches the cores that the guest is using. Maybe
> this is not worth trying anyway? It seems to suggest that the USB ASIO
> driver for the MG10-XU has issues with timing that are impacted by not
> enough CPU cycles.
>  

> It must be more than that though, because it seems to also cut out and
> skip relentlessly with mpeg (x264 specifically.) In a lot of games the
> sound tends to skip during cinematics and  some high bandwidth movies
> consistently cause this problem.
>  

> However, I can get audio playback up to 192khz FLAC working but the
> driver usually crashes after a while and usually requires the whole
> system to be pretty idle. The mixer driver doesn’t crash like that on
> other computers. Both the VGA card and USB card are situated in PCIe
> slots adjacent to the same CPU in the NUMA topology however I’m not
> making any changes to the NUMA configuration at runtime, I tried
> without finding that it made any difference.
>  

> I used to have another USB card but that one did the same thing.
> Everything else that I could possibly care about works fantastic,
> including the mouse responsiveness—I have a whole powered hub of USB
> devices including an xBox controller connected to the USB card all of
> which work great. Games work really well in 1080p at 120hz. I would try
> to pass the mixer through VIA USB redirection (same way I’m doing the
> corsair PSU) but it wouldn’t work and I don’t imagine it would be much
> better. I’ve also tried getting my Scarlett 2i2 with it but I have the
> same kind of problems and it typically doesn’t work for more than 20
> seconds at a time.
>  

> Any thoughts or information you have to share would be appreciated.
> I’d be happy to try and debug this some more but I’m completely out of
> ideas of where to go. It’s an interesting problem to say the least. I
> have tried a a lot of different things except those that I can’t
> really try. Please get in touch if you have any ideas.
>  

> Thank you,

>  

> -Paige

>  

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