Re: Windows 10 passthrough lag/micro-freeze issues during disk I/O

[Lukas Straub]

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On Fri, 20 Mar 2020 15:46:45 -0400
Jérôme Poulin <address@hidden> wrote:

> Hi everyone,
> 
> I have a VM right now that is setup as my gaming machine with video
> pass-through, it works perfectly except when there's I/O on the host.
> 
> When there is I/O, the VM will have micro-freeze events where everything
> locks up for milliseconds up to a second at a time at frequent intervals,
> the host is on NVMe, CPUs are pinned with a dedicated core for emulator.
> 
> Whatever I put, virtio, virtio-scsi, cache=none, cache=writeback, threads
> or native, as soon as there is I/O, I get the same problem, to the point
> where it causes disconnections on the virtual USB bus.
> 
> VM is setup with hugepages, CPU pinning, I tried making qemu threads
> realtime with no success (even blue screens). I tried with dedicated cores
> (isolcpus), i440/q35, now I'm out of ideas. I do run a custom kernel to be
> able to use pcie_acs_override=downstream,multifunction in GRUB because I
> can't use passthrough otherwise.
> 
> This problem has been following me from my old setup to my new setup
> Old setup:
> ASUS B150 PLUS USB3
> Core i7 6700K
> 16 GB DDR3
> SATA raw LVM volume for Windows
> 
> New setup
> ASRock Z390 Taichi
> Core i7 9700K
> 48 GB DDR4
> NVMe raw LVM volume for Windows
> 
> Any ideas would be appreciated.
> 

Have you tried putting qemu in the realtime I/O-scheduling class via ionice?

Regards,
Lukas Straub
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