On 6/25/17 12:55, Nick Sarnie wrote:
On Fri, May 5, 2017 at 1:27 PM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
On Wed, 3 May 2017 12:28:35 -0400
Nick Sarnie <commendsarnex@xxxxxxxxx> wrote:
On Wed, May 3, 2017 at 10:37 AM, Matthias Ehrenfeuchter <efeu@xxxxxxxxxx> wrote:
Hi,
There are a lot of messages/threads out there about bad performance while
using AMDs Ryzen with KVM GPU passthrough. It revolves all on
enabling/disabling npt, while enabled overall VM performance is nice but the
GPU performance gives me about 20% (and a lot of drops to zero GPU usage,
while CPU/Disk/Ram also doing nothing) compared to npt disabled. But while
npt is disabled overall VM performance is like beeing on 4x86 with floppy
disk as only storage. (Ex. it takes 2 seconds just to open startmenu while
host and vm are in idle, and neither CPU pinning, changing CPU model,
changing storage device nor using hugepages changed anything).
So everything I read pointed to a bug in the npt implementation? Anything I
could do to get closer to the "thing" issuing this?
Best Regards
efeu
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I heard from Joerg that it might be related to a lower intercept rate
being used when NPT is enabled, but we haven't been able to find a way
to trace that to confirm.
Joerg/Paolo, any ideas how we might debug this? Anyone from AMD
watching? Thanks,
Alex
Hi all,
A somewhat major update.
I managed to install Xen with my GPU passthrough config and test the
performance with NPT enabled.
There is no performance drop with NPT on Xen, it matches the GPU
performance of KVM with NPT disabled. The CPU performance is also
great.
John Bridgman (ccd) from AMD says he's going to ask around AMD about
this next week, but it would be even better if some AMD guys that read
this ML shared their ideas or took a look.
Let me know if you need any more information.
Thanks,
Sarnex
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So, I'm trying to reproduce this issue on the Ryzen system w/ the following setup:
* Host kernel v4.11 (with this patch https://lkml.org/lkml/2017/6/23/295)
* guest VM RHEL7.3
* guest graphic driver = radeon
* qemu-system-x86_64 --version
QEMU emulator version 2.9.50 (v2.9.0-1659-g577caa2-dirty)
* kvm-amd npt=1
* dGPU is 08:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
[AMD/ATI] Tobago PRO [Radeon R7 360 / R9 360 OEM] (rev 81)
* qemu-system-x86_64 -smp 4 -enable-kvm -M q35 -m 4096 -cpu host -bios
/usr/share/qemu/bios.bin -device
ioh3420,bus=pcie.0,addr=1c.0,multifunction=on,port=1,chassis=1,id=root.1 -drive
file=/sandbox/vm-images/rhel7.3.qcow2,if=virtio,id=disk0 -net none -vga none
-nodefaults -device
vfio-pci,host=08:00.0,x-vga=on,addr=0.0,multifunction=on,bus=root.1,romfile=/sandbox/vm-images/vbios.rom
-usb -device usb-host,hostbus=3,hostport=1 -device usb-host,hostbus=3,hostport=3
-device vfio-pci,host=0000:08:00.1 -device vfio-pci,host=0000:09:00.0
With this setup, I am able to pass-through the dGPU and run the following test:
* Starting up the guest w/ full GNOME GUI on the attached monitor.
* glxgears (running @ 60 FPS)
* Playing 1080p HD video on Youtube
I am not noticing issues here. What kind of test are you running in the guest VM?
Thanks,
Suravee
