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
