[Bug 1703506] Re: SMT not supported by QEMU on AMD Ryzen CPU

[Anthony Kamau]

I was able to avoid rebooting after following @Andrii's instructions -
https://bugs.launchpad.net/qemu/+bug/1703506/comments/19 - above:

systemctl stop libvirtd libvirtd-admin.socket libvirtd-ro.socket libvirtd.socket
sudo modprobe -r kvm_intel kvm
systemctl start libvirtd libvirtd-admin.socket libvirtd-ro.socket 
libvirtd.socket

These instructions to avoid rebooting might not work for those using a
non-Intel CPU as you'll have a different kernel module.  You can check
by running `lsmod | grep kvm`.

Cheers,
ak.

System info:
# inxi -CMz
Machine:
  Type: Laptop System: Dell product: Precision M6700 v: 01 serial: <filter>
  Mobo: Dell model: 0JWMFY v: A00 serial: <filter> UEFI: Dell v: A20 date: 
11/30/2018
CPU:
  Info: quad core model: Intel Core i7-3840QM bits: 64 type: MT MCP cache: L2: 
1024 KiB
  Speed (MHz): avg: 3607 min/max: 1200/3800 cores: 1: 3588 2: 3615 3: 3638 4: 
3588 5: 3588
    6: 3638 7: 3617 8: 3588

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https://bugs.launchpad.net/bugs/1703506

Title:
  SMT not supported by QEMU on AMD Ryzen CPU

Status in QEMU:
  Expired

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

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