[vfio-users] R9 380 Performance Issues

Alexander Epp alex at piconino.de
Tue Apr 5 17:53:39 UTC 2016

You need to pin the cores. And you should not use the ht-siblings for
the guest, but for emulator. Something like:

  <vcpu placement='static'>6</vcpu>
    <vcpupin vcpu='0' cpuset='2'/>
    <vcpupin vcpu='1' cpuset='3'/>
    <vcpupin vcpu='2' cpuset='4'/>
    <vcpupin vcpu='3' cpuset='5'/>
    <vcpupin vcpu='4' cpuset='6'/>
    <vcpupin vcpu='5' cpuset='7'/>
    <emulatorpin cpuset='10-15'/>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='6' threads='1'/>

see Alex's notes at

Am 04.04.2016 um 06:37 schrieb Froz --:
> Running into some issues with passing through an R9 380 (besides the usual reset 
> bug). Processor's a 5960x, if that's relevant.
> First up, I'm running Arch Linux on kernel 4.4.5. For what it's worth, the 
> issues occurred on the latest Fedora kernel, too.
> I'm using OVMF rather than VGA, vfio-pci only, no pci-stub. The passthrough 
> itself works, using either libvirt or QEMU directly. However, I'm only seeing 
> ~60% of native GPU performance running benchmarks in the VM. Other than that, 
> the VM performs fine (although it takes an oddly long time to boot).
> My QEMU options are as follows:
> taskset -ac 4-15 qemu-system-x86_64 \
>      -name Win10 \
>      -enable-kvm \
>      -nodefaults \
>      -nodefconfig \
>      -rtc base=localtime \
>      -cpu host \
>      -smp sockets=1,cores=6,threads=2 \
>      -m 24756 \
>      -soundhw hda \
>      -serial none \
>      -parallel none \
>      -drive 
> if=pflash,format=raw,readonly,file=/usr/share/edk2.git/ovmf-x64/OVMF_CODE-pure-efi.fd 
> \
>      -drive if=virtio,format=raw,cache=none,aio=native,file=/dev/guests/win10 \
>      -device vfio-pci,host=02:00.0,multifunction=on \
>      -device vfio-pci,host=02:00.1 \
>      -usb -device usb-host,hostbus=2,hostaddr=4 \
>      -usb -device usb-host,hostbus=2,hostaddr=3
> Both the devices I'm passing through constitute a whole IOMMU group.
> dmesg doesn't bring up any errors. To be honest, I'm not sure how to begin 
> deciphering this, as you can probably tell. This is the first time I've 
> attempted GPU passthrough, on a new system, and after reading about the 
> workarounds necessary to get nvidia cards working I figured AMD was the better 
> choice. Clearly I was wrong!
> Did I make an (expensive!) mistake in purchasing a R9 380, or have other people 
> had better luck? Does anyone know how to go about improving performance? I 
> haven't experimented with hugepages, but the problem seems to be solely 
> "graphical" in nature. CPU pinning doesn't seem to make any difference, as you'd 
> expect.
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