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[Qemu-devel] [Bug 1703506] Re: SMT not supported by QEMU on AMD Ryzen CP

From: Eduardo Habkost
Subject: [Qemu-devel] [Bug 1703506] Re: SMT not supported by QEMU on AMD Ryzen CPU
Date: Thu, 13 Dec 2018 16:08:12 -0000

@ryzen27: do you have dmesg logs showing the MSRs being written by the
guest? You may be hitting the bug described at

** Bug watch added: Red Hat Bugzilla #1592276

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  SMT not supported by QEMU on AMD Ryzen CPU

Status in QEMU:

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

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