Re: Multiple monitors at 4K, in virt-manager?

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On 3/22/21 5:27 PM, Dr. Jennifer Nussbaum wrote:
On Monday, March 22, 2021, 10:51:48 AM EDT, Victor Toso <victortoso@xxxxxxxxxx> wrote:


On Mon, Mar 22, 2021 at 01:46:08PM +0000, Dr. Jennifer Nussbaum wrote:

 > > I'm using virt-manger, and its related suite of stuff, to run
 > > KVM/QEMU VM's on a Debian Bullseye host, which has two 4K
 > > monitors. I am unable to get dual-head working at all, and I
 > > can't get 4K resolution working in the way I'm apparently
 > > supposed to.
 > Can you share the vm's domain? virsh dumpxml $vm

I've posted this at the bottom of this message, with only small changes to obscure the UUID and paths.

 > > I have a Debian Bullseye guest, with spice-vdagent and the QXL
 > video drivers installed in it. The Spice user manual suggests
 > that multiple-monitor support is easy; you're supposed to use a
 > Video QXL device and then everything should just work. But it
 > doesn't. Even when I increase the video memory in the XML file
 > (vgamem, I assume) to 64MB I am unable to get 4K on even a
 > single monitor using Settings -> Display on the guest; it maxes
 > out at some arbitrary-seeming thing a bit over 1980 x 1200. And
 > regardless of resolution, I also do not have a second monitor
 > available in the guest.


It seems 64MB is not enough.

4096 * 2160 * 4 * 2 > 64MB

Can you try replacing all those 64MB below with 128MB ?
Please try with 1 head first. Possibly 2 heads need
more (but not for all params).


 > Are you accessing with virt-manager? I don't think there is
 > support for multi-monitor there? You should use virt-viewer or
 > remote-viewer instead.

virt-manager uses virt-viewer natively; it's what virt-manager fires up when you use the "view graphical console" option.

Regardless, I did just launch virt-viewer separately, and it's functioning in the same way.

 > If I have a video device set to Virtio, then 4K works perfectly
 > on the guest machine; if I go to Settings -> Display there, I
 > can select 4096 x 2160, and I get lovely 4K video. However,
 > dual-head does not work. If I try to edit the XML for the video
 > device to 'heads="2"', there is no effect--at least, when I
 > restart the guest and go to Settings -> Display, there isn't an
 > option for selecting another monitor.  Could someone tell me
 > what I'm supposed to be doing?  Thank you.

Just confirming, for Spice multi-monitor [0] in recent linux
guests, one qxl device is enough and you should set the heads to
2 (virsh edit $vm)

As you can see from the XML below, I do (think I) have one qxl device, with 2 heads and 64MB memory.

When I go into the guest, the maximum resolution I am offered is 2952 x 1781. And there is only one display,
called "Virtual-0".

Thank you for looking this over.



<domain type="kvm">
   <memory unit="KiB">4194304</memory>
   <currentMemory unit="KiB">4194304</currentMemory>
   <vcpu placement="static">2</vcpu>
     <type arch="x86_64" machine="pc-i440fx-2.8">hvm</type>
     <boot dev="hd"/>
     <vmport state="off"/>
   <cpu mode="host-model" check="partial"/>
   <clock offset="utc">
     <timer name="rtc" tickpolicy="catchup"/>
     <timer name="pit" tickpolicy="delay"/>
     <timer name="hpet" present="no"/>
     <suspend-to-mem enabled="no"/>
     <suspend-to-disk enabled="no"/>
     <disk type="file" device="disk">
       <driver name="qemu" type="qcow2"/>
       <source file="/home/user/VMs/debian-bullseye-clone.qcow2"/>
       <target dev="vda" bus="virtio"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x07" function="0x0"/>
     <disk type="file" device="cdrom">
       <driver name="qemu" type="raw"/>
       <target dev="hda" bus="ide"/>
       <address type="drive" controller="0" bus="0" target="0" unit="0"/>
     <controller type="usb" index="0" model="ich9-ehci1">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x05" function="0x7"/>
     <controller type="usb" index="0" model="ich9-uhci1">
       <master startport="0"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x05" function="0x0" multifunction="on"/>
     <controller type="usb" index="0" model="ich9-uhci2">
       <master startport="2"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x05" function="0x1"/>
     <controller type="usb" index="0" model="ich9-uhci3">
       <master startport="4"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x05" function="0x2"/>
     <controller type="pci" index="0" model="pci-root"/>
     <controller type="ide" index="0">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x1"/>
     <controller type="virtio-serial" index="0">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x06" function="0x0"/>
     <interface type="network">
       <mac address="52:54:00:30:01:2b"/>
       <source network="default"/>
       <model type="rtl8139"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x0"/>
     <serial type="pty">
       <target type="isa-serial" port="0">
         <model name="isa-serial"/>
     <console type="pty">
       <target type="serial" port="0"/>
     <channel type="unix">
       <target type="virtio" name="org.qemu.guest_agent.0"/>
       <address type="virtio-serial" controller="0" bus="0" port="1"/>
     <channel type="spicevmc">
       <target type="virtio" name="com.redhat.spice.0"/>
       <address type="virtio-serial" controller="0" bus="0" port="2"/>
     <input type="tablet" bus="usb">
       <address type="usb" bus="0" port="1"/>
     <input type="mouse" bus="ps2"/>
     <input type="keyboard" bus="ps2"/>
     <graphics type="spice" autoport="yes">
       <listen type="address"/>
       <image compression="off"/>
     <sound model="ich6">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x04" function="0x0"/>
      <model type="qxl" ram="65536" vram="65536" vgamem="65536" heads="2" primary="yes"/>       <address type="pci" domain="0x0000" bus="0x00" slot="0x09" function="0x0"/>
     <redirdev bus="usb" type="spicevmc">
       <address type="usb" bus="0" port="2"/>
     <redirdev bus="usb" type="spicevmc">
       <address type="usb" bus="0" port="3"/>
     <memballoon model="virtio">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x08" function="0x0"/>

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