[vbox-dev] Monitor count limitations
Rūdolfs Bundulis
rudolfs.bundulis at gmail.com
Wed Aug 27 17:46:29 GMT 2014
Hi,
> Which guest OS are you using? Which driver did you install (for those
> OSes which allow selecting)?
I am running Windows 7, but I seems that I also have a Xubuntu 14 machine
and I could set up a Windows XP machine to see if that fits better. I
installed the default guest additions package on both Windows 7 and
Xubuntu, on Windows7 i checked the Direct3D checkbox.
> Barely... the above formula gives 223MB already, and if the Windows
> driver really need the mentioned amount of offscreen memory you'd run
> out of VRAM. I'd use VBoxHeadless to try this out actually, because it
> doesn't have any of those annoying safeguards to protect users from
> shooting themselves in the foot.
Ok that could explain why I don't get the full hd resolutions, I could be
just simply running out of VRAM. VboxHeadless wont help, I already have a
console app that starts the VM using the COM API and injects implementation
for the IFramebuffer interfaces in each monitor and I capture the display
surfaces. So it seems that 25 full hd displays on Windows is not possible.
Best Regards,
Rudolfs Bundulis
2014-08-27 20:11 GMT+03:00 Klaus Espenlaub <klaus.espenlaub at oracle.com>:
> On 27.08.2014 18:38, Rūdolfs Bundulis wrote:
> > Hi Klaus,
> >
> > Thanks again for the fast response. Well, this is a university research
> > project to build monitor walls without the underlying hardware, so I
> > guess its reasonable that I am breaking some limits that should be
> > normal in a normal use case.
>
> As long as you're only going for high monitor counts, that's nothing
> unexpected.
>
> > Regarding 3D, when I installed guest additions I checked the Direct3D
> > box but I dont have the "Enable 3D acceleration" checkbox checked in
> > the VirtualBox manager. Should I reinstall the guest additions without
> > Direct3D?
>
> Strange... I wonder why the GUI is so eager with insanely high VRAM
> proposals. It should only care about the checkbox, because if that's not
> set then there is no 3D, period.
>
> From what I remember, the "rule of thumb" for the absolute minimum VRAM
> size (in bytes) is (x*y*4+4096+1048576)*count. At least it was accurate
> with the X11 driver, and the GUI seems to agree. It seems the XPDM
> driver needs twice that much (because Windows needs one offscreen
> surface), and with the WDDM driver it needs thrice that much (two
> offscreen surfaces).
>
> Which guest OS are you using? Which driver did you install (for those
> OSes which allow selecting)?
>
> > And more important, is it actually possible to fit 25 full hd
> > (1920x1080) framebuffers in the video ram if it is only 256mb inside
> > virtualbox? I could try to recompile from sources with lets say 1GB if
> > redefining the video memory macro does not break other stuff.
>
> Barely... the above formula gives 223MB already, and if the Windows
> driver really need the mentioned amount of offscreen memory you'd run
> out of VRAM. I'd use VBoxHeadless to try this out actually, because it
> doesn't have any of those annoying safeguards to protect users from
> shooting themselves in the foot.
>
> Increasing the VRAM size by recompiling will cause trouble, as it would
> need drastic changes to the memory layout (PCI memory hole, ...), and
> I'm quite sure that we looked at it and considered it too much effort.
> Everything is doable in the end, that's the good and bad thing about
> software :)
>
> Klaus
>
> > Best Regards,
> > Rudolfs Bundulis
> > From: Klaus Espenlaub
> > Sent: 2014.08.27. 19:05
> > To: vbox-dev at virtualbox.org
> > Subject: Re: [vbox-dev] Monitor count limitations
> > Hi Rūdolfs,
> >
> > On 27.08.2014 16:49, Rūdolfs Bundulis wrote:
> >> Hi,
> >>
> >> I've run into some more issues with high monitor count on VirtualBox.
> >> Basically when selecting 25 displays it complains that at least 600
> >> something MB of VRAM is needed, but while the arrows in the display
> >> number box allow to select more than 8 monitors, seems that i can't go
> >> above 256 mb in VRAM. Is this a hard limitation? Since the COM API also
> >> does not allow me to set more than that.
> >
> > Sounds like you have 3D enabled - then the GUI does a little too simple
> > maths, extrapolating the necessary space beyond sanity. It's only a
> > proposal, not a hard "must have". Don't think anyone tried to go to such
> > extremes, because it's just nonsense to expect even basic 3D able to
> > cope with so many screens.
> >
> > If you disable 3D then the requirements should be a lot lower, in the
> > order of what's needed to represent the pixels.
> >
> > Yes, there is currently a hard limit of 256 MiB VRAM, and we didn't find
> > cases where it was absolutely necessary to have more.
> >
> > Klaus
> >> Best Regards,
> >> Rudolfs Bundulis
> >>
> >>
> >> 2014-06-18 13:41 GMT+03:00 Rūdolfs Bundulis <rudolfs.bundulis at gmail.com
> >> <mailto:rudolfs.bundulis at gmail.com>>:
> >>
> >> Hi Klaus,
> >>
> >> Thanks a lot for the clarification. I thought the same that it was
> >> just a sanity limit, but in my case this is really needed. Then I
> >> guess will be able to do the same with the COM API, thanks a lot
> again.
> >>
> >>
> >> 2014-06-18 13:13 GMT+03:00 Klaus Espenlaub
> >> <klaus.espenlaub at oracle.com <mailto:klaus.espenlaub at oracle.com>>:
> >>
> >> Hi Rūdolfs,
> >>
> >> On 18.06.2014 11:48, Rūdolfs Bundulis wrote:
> >> > Hi,
> >> >
> >> > I'm developing a system that needs to run a headless VM with
> >> a large
> >> > number of attached monitors - currently the GUI has the
> limit
> >> to set
> >> > maximum monitor count to 8, I didn't check the COM API
> myself
> >> but I
> >> > suspect that it will not allow me to set the count greater
> >> than 8, while
> >> > browsing the VirtualBox sources show that the internal C
> macro is
> >> > defined to 64:
> >> >
> >> > /* this should be in sync with monitorCount
> <xsd:maxInclusive
> >> > value="8"/> in
> >> src/VBox/Main/xml/VirtualBox-settings-common.xsd */
> >> > #define VBOX_VIDEO_MAX_SCREENS 64
> >>
> >> Looks to me that this comment is simply outdated. Nothing more,
> >> nothing
> >> less.
> >>
> >> Many limits can be listed with "VBoxManage list
> >> systemproperties", and
> >> it shows 64.
> >>
> >> > Is there really a need to limit the count to 8? If I change
> >> the xml
> >> > schema file and increase the count from 8 to 64 and
> recompile
> >> would
> >> > there be any actual limitations in the VirtualBox core?
> >>
> >> There is a constant conflict in the GUI between sanity (i.e.
> >> protecting
> >> users against their stupidity - you can't believe how many
> people
> >> believe that more is better, even if it's a giant waste of
> resources
> >> instead) and allowing expert users to go to the extreme. There
> are
> >> extremely few people out there who ever need to deal with more
> >> than 8
> >> monitors.
> >>
> >> In my quick test I could use the GUI to select 20 monitors -
> >> sure, the
> >> slider doesn't allow that, but one can enter the number or use
> the
> >> up/down arrows. This needs 256MB of VRAM, which this high
> number
> >> automatically unlocks.
> >>
> >> Klaus
> >>
> >
>
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