I can confirm the same behavior with a Ryzen 7 1700. Host Arch Linux x64 Kernel 4.11.9, Guest Windows 10 Pro. Running with -cpu host and -smp 8,sockets=1,cores=4,threads=2. Attached the logs of the host and results of the output of msinfo32 and "WMIC CPU Get NumberOfCores,NumberOfLogicalProcessors /Format:List" in the guest. Same results as scix, in my case 8 Core(s), 8 Logical Processors(s).
This seems relevant: https://bugzilla.redhat.com/show_bug.cgi?id=1135772 And a few extra reports on reddit: https://www.reddit.com/r/VFIO/comments/6nuhb5/big_problem_with_my_ryzen_1700x/ https://www.reddit.com/r/VFIO/comments/6m6kry/smthyperthreading_support_with_ryzen_cpu_and/ I'll test with a Linux guest later. ** Bug watch added: Red Hat Bugzilla #1135772 https://bugzilla.redhat.com/show_bug.cgi?id=1135772 ** Attachment added: "smt-ryzen.zip" https://bugs.launchpad.net/qemu/+bug/1703506/+attachment/4917550/+files/smt-ryzen.zip -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1703506 Title: SMT not supported by QEMU on AMD Ryzen CPU Status in QEMU: New Bug description: HyperThreading/SMT is supported by AMD Ryzen CPUs but results in this message when setting the topology to threads=2: qemu-system-x86_64: AMD CPU doesn't support hyperthreading. Please configure -smp options properly. Checking in a Windows 10 guest reveals that SMT is not enabled, and from what I understand, QEMU converts the topology from threads to cores internally on AMD CPUs. This appears to cause performance problems in the guest perhaps because programs are assuming that these threads are actual cores. Software: Linux 4.12, qemu 2.9.0 host with KVM enabled, Windows 10 pro guest To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1703506/+subscriptions