How can I make use of QEMU's shared memory & hyper-v support with a Quickemu configuration file?

[seltzered]

I recently setup a new Virtual machine (linux host, windows guest) with Virtual Machine Manager following guides like https://sysguides.com/install-a-windows-11-virtual-machine-on-kvm which go into some specifics on setting things up for hyper-v enlightenments , shared memory, and more, realizing this might have some performance benefits over a standard quickemu setup.

How can I improve my existing quickemu configuration (e.g. windows.conf file) to make use of some of these options? I've tried looking around and while there's advice specific to direct qemu command-line options and VMM I hadn't seen any explicit guidance when using quickemu .conf files.

[seltzered]

Taking inspiration from https://sysguides.com/install-a-windows-11-virtual-machine-on-kvm , https://www.reddit.com/r/linuxquestions/comments/u3fs09/comment/jpbs8il/ , and of course https://github.com/quickemu-project/quickemu/wiki/05-Advanced-quickemu-configuration , there's a few things to do here:

• On your linux host: Setup Kernel-based Virtual Machine (KVM) virtualization support if you haven't already, see the guide here: https://sysguides.com/install-kvm-on-linux .

• On your linux host: Setup ksmtuned - ie. sudo dnf install ksmtuned ( based on https://www.reddit.com/r/linuxquestions/comments/u3fs09/what_is_enable_shared_memory_option_in/ )

• Assuming you already have a quickemu .conf file, you'll need to add something like the following for extra-args, which is basically args for QEMU (this example is for an Intel processor, linux host, windows 10/11 guest):

  • extra_args="--enable-kvm --cpu host,hv_relaxed,hv_vapic,hv_spinlocks=8191,hv_vpindex,hv_runtime,hv_synic,hv_time,hv_stimer,hv_stimer_direct,hv_reset,hv_frequencies,hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs --machine q35,memory-backend=pc.ram --object qom-type=memory-backend-memfd,id=pc.ram,share=true,x-use-canonical-path-for-ramblock-id=false,size=4G"
  • Okay, so there's a lot in that line above, let's try to break it down:
    • --enable-kvm and --cpu host,hv_relaxed,hv_vapic,hv_spinlocks=8191,hv_vpindex,hv_runtime,hv_synic,hv_time,hv_stimer,hv_stimer_direct,hv_reset,hv_frequencies,hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs is largely doing the suggestions in https://sysguides.com/install-a-windows-11-virtual-machine-on-kvm from section '1.3. Enable Hyper-V Enlightenments'. This may vary depending on your cpu vendor (e.g. AMD, Intel) & architecture. More documentation is in https://www.qemu.org/docs/master/system/i386/hyperv.html
    • --machine q35,memory-backend=pc.ram and --object qom-type=memory-backend-memfd,id=pc.ram,share=true,x-use-canonical-path-for-ramblock-id=false,size=4G are used for setting up shared memory. You may want to play around and see what your memory footprint looks like with and without these settings. The size=4G may depend on what you have separate let for your ram (e.g. I also have ram="4G")

With all this in mind, you may end up with a quickemu conf file like this:

guest_os="windows"
disk_img="windows-10/disk.qcow2"
iso="windows-10/MY_WINDOWS_ISO.iso"
fixed_iso="windows-10/virtio-win.iso"
width="1024"
height="768"
mouse="virtio"
ram="4G"
viewer="spicy"
display="spice"
extra_args="--enable-kvm --machine q35,memory-backend=pc.ram --cpu host,hv_relaxed,hv_vapic,hv_spinlocks=8191,hv_vpindex,hv_runtime,hv_synic,hv_time,hv_stimer,hv_stimer_direct,hv_reset,hv_frequencies,hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs --object qom-type=memory-backend-memfd,id=pc.ram,share=true,x-use-canonical-path-for-ramblock-id=false,size=4G"