AnsweredAssumed Answered

KVM GPU passthrough (IOMMU) issue on Ryzens AMD-V

Question asked by efeu on May 12, 2017
Latest reply on Jun 22, 2019 by gb_l_fr



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?


We've been discussing about this problem in community for a while now, but noone could find out the reason for this. 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.


Also wondering if this is an hardware related issue on Ryzens AMD-V, so the upcoming Naples does have it too? This would be a nogo for the server platform and, in my eyes, the death even pre-released. I hope someone from AMD can help here, this is a huge disadvantage on the Ryzen chips, and if not beeing resolved soon, I have to switch back to Intel as only option, beeing not alone with this...


Best Regards