[vbox-dev] Monitor count limitations

Klaus Espenlaub klaus.espenlaub at oracle.com
Thu Sep 4 09:23:45 GMT 2014


On 04.09.2014 11:04, Rūdolfs Bundulis wrote:
>> Good to know that it works!
> Well, without the advices form you and Klaus I wouldn't have gone far,
> so great thanks:) Btw, this is not that important, but since I plan to
> host any OS with the wall, does OS X have any special tweaks like the
> windows WDDM/XPDM that I should now about? So far I've checked Windows
> and XFCE and they both worked fine, but Klaus arleady warned me that X11
> is less resource hungry than Windows. Does OS X fall into the same
> category as X11?

Today OS X in a VirtualBox VM is the very opposite of VRAM hungry. We 
don't have any graphics driver for it, which means it runs using purely 
the UEFI graphics support. To my knowledge this is limited to a single 

We're planning to do an OS X graphics driver (as part of an eventually 
complete set of guest additions), but as there doesn't seem to be any 
potential paying customers it can't get a high priority.


> 2014-09-04 11:49 GMT+03:00 Vitali Pelenjow <Vitali.Pelenjow at oracle.com
> <mailto:Vitali.Pelenjow at oracle.com>>:
>     Good to know that it works!
>     Thanks,
>     Vitali.
>     Rūdolfs Bundulis wrote:
>         Hi Vitali,
>         no it does not. And I just found the issue, the H264 encoder was
>         actually stalling after the 1280x720 resize on all 25 monitors
>         and since I was checking this from home and I did not have
>         access to the actual wall, I did not see that. I fixed it an
>         yeah, now I got all 25 to resize to full hd, after they were all
>         resized to 1280x720. So with XPDM the VRAM amount is sufficient
>         for my needs. Seems that I'll have to stack multiple GPU's or
>         combine GPU/CPU encdoing to actually be able to pull this amount
>         of pixels off at 25fps. Sorry for that, I hope I didn't take too
>         much of your time with the verifications done on your side  and
>         thank you both (you and Klaus) for the info - the XPDM thing was
>         very important, now I can run all the 5x5 wall with full hd.
>         Best Regards,
>         Rudolfs Bundulis
>         2014-09-04 10:43 GMT+03:00 Vitali Pelenjow
>         <Vitali.Pelenjow at oracle.com <mailto:Vitali.Pelenjow at oracle.com>
>         <mailto:Vitali.Pelenjow at __oracle.com
>         <mailto:Vitali.Pelenjow at oracle.com>>>:
>              Does the VM have 2d acceleration enabled (in the VM settings)?
>              Which version of VBox/guest addidions do you use?
>              Please also send me VBox.log of the VM with 25 monitors.
>              And the VM xml config file (VMNAME.vbox).
>              I tried with current VBox trunk. Used one of existing Win7
>         32 bit
>              VMs with XPDM driver.
>              I edited the .vbox xml config to set 256MB VRAM and 24
>         monitors.
>              Then started the VM with VBoxHeadless and on the host executed
>              a batch script with VBoxManage controlvm setvideomodehint
>         for each
>              monitor.
>              Then connected to the VMs first monitor with a RDP client and
>              checked that
>              Display Properties in the guest show all 24 monitors at
>         1920x1200.
>              Vitali
>              Rūdolfs Bundulis wrote:
>                  >I wonder why monitors in your guest resize to 1280x720.
>                  >Did you allow all modes in
>         IFramebuffer::__VideoModeSupported?
>                  >Can you run 1 monitor at 1920x1200?
>                  >How do you resize the guest monitors: from the guest
>         or using
>                  VBoxManage
>                  >controlvm setvideomodehint?
>                  And I try to force the desired resolution like this:
>                  for (unsigned short nMonitorIndex = 0; nMonitorIndex <
>                  m_nMonitorCount; ++nMonitorIndex)
>                  {
>                  // Set full hd for all the screens
>         CHECK_HRESULT(m_pDisplay->__SetVideoModeHint(__nMonitorIndex,
>                  true, false, 0, 0, 1920, 1080, 32));
>                  }
>                  One monitor runs fine, 7 also work, I didn't have time
>         now to
>                  find exact boundary but I will do it. Bascially in all the
>                  configuriation the VirtualBox logs shows the hint for
>                  1920x1080 but a bit later just resizes to 1280x720 and does
>                  not even try that. I'll mail you the source and logs
>         directly,
>                  thanks for the help.

More information about the vbox-dev mailing list