Hi all, Myself and many community members have noticed an issue when enabling Nested Page Tables in a VM which uses GPU Passthrough on AMD CPUs. I have found that NPT universally increases CPU performance when it is enabled, but it destroys passed-through GPU performance by around two to three times depending on the application. For example, my Dota 2 FPS with NPT enabled is around 30 FPS, where as it is around 110 FPS with NPT disabled. This has been reproduced by myself on both Linux and Windows VMs, is widely reported in the VFIO community, and Alex Williamson told me that he was able to reproduce the issue on both AMD and Nvidia GPUs, but isn't sure of the cause.
Because of this, we are forced to disable NPT if we want to have any sort of reasonable GPU performance, which in turn causes CPU performance issues. Please let me know if you have any ideas on this issue, I can test any patches or provide any more information. Thank you, Nick Sarnie _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
