AMD Ryzen KVM/NPT/IOMMU issue

I have identified the issue! With NPT enabled I am now getting near bare metal performance with PCI pass through. The issue was with some stubs that have not been properly implemented. I will clean my code up and submit a patch shortly. This is a 10 year old bug that has only become evident with the recent ability to perform PCI pass-through with dedicated graphics cards. I would expect this to improve performance across most workloads that use AMD NPT. Here are some benchmarks to show what I am getting in my dev environment: https://www.3dmark.com/3dm/22878932 https://www.3dmark.com/3dm/22879024 -Geoff On 2017-10-24 16:15, geoff at hostfission.com wrote: > Further to this I have verified that IOMMU is working fine, traces and > additional printk's added to the kernel module were used to check. All > accesses are successful and hit the correct addresses. > > However profiling under Windows shows there might be an issue with IRQs > not reaching the guest. When FluidMark is running at 5fps I still see > excellent system responsiveness with the CPU 90% idle and the GPU load > at 6%. > > When switching PhysX to CPU mode the GPU enters low power mode, > indicating that the card is no longer in use. This would seem to > confirm that the GPU is indeed in use by the PhysX API correctly. > > My assumption now is that the IRQs from the video card are getting > lost. > > I could be completely off base here but at this point it seems like the > best way to proceed unless someone cares to comment. > > -Geoff > > > On 2017-10-24 10:49, geoff at hostfission.com wrote: >> Hi, >> >> I realize this is an older thread but I have spent much of today >> trying to >> diagnose the problem. >> >> I have discovered how to reliably reproduce the problem with very >> little effort. >> It seems that reproducing the issue has been hit and miss for people >> as it seems >> to primarily affect games/programs that make use of nVidia PhysX. My >> understanding of npt's inner workings is quite primitive but I have >> still spent >> much of my time trying to diagnose the fault and identify the cause. >> >> Using the free program FluidMark[1] it is possible to reproduce the >> issue, where >> on a GTX 1080Ti the rendering rate drops to around 4 fps with npt >> turned on, but >> if turned off the render rate is in excess of 60fps. >> >> I have produced traces for with and without ntp enabled during these >> tests which >> I can provide if it will help. So far I have been digging through how >> npt works >> and trying to glean as much information as I can from the source and >> the AMD >> specifications but much of this and how mmu works is very new to me so >> progress >> is slow. >> >> If anyone else has looked into this and has more information to share >> I would be >> very interested. >> >> Kind Regards, >> Geoffrey McRae >> HostFission >> https://hostfission.com >> >> >> [1]: >> http://www.geeks3d.com/20130308/fluidmark-1-5-1-physx-benchmark-fluid-sph-simulation-opengl-download/