On Wed, Jun 28, 2017 at 1:23 PM, Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx> wrote: > > > 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 >>>>> _______________________________________________ >>>>> iommu mailing list >>>>> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx >>>>> https://lists.linuxfoundation.org/mailman/listinfo/iommu >>>> >>>> >>>> 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 >> _______________________________________________ >> iommu mailing list >> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx >> https://lists.linuxfoundation.org/mailman/listinfo/iommu >> > > 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? Try running the open source game "torcs" inside the VM. I think you'll find that there's a very noticeable performance different between npt=1 and npt=0 -- -Steven Walter <stevenrwalter@xxxxxxxxx>
