[vbox-dev] Monitor count limitations
Rūdolfs Bundulis
rudolfs.bundulis at gmail.com
Mon Sep 1 19:23:59 GMT 2014
Hi,
any hints on how to understand if a Windows 7 guest OS uses XPDM or WDDM
driver? I would be interrested to see if with XPDM I can actually reduce
the needed memory for the surfaces.
2014-08-28 23:03 GMT+03:00 Rūdolfs Bundulis <rudolfs.bundulis at gmail.com>:
> Btw, here is a little demo of the 16 * 720p wall driven by virtualbox
>
> https://www.youtube.com/watch?v=eFAATNofjHA&feature=youtu.be
>
>
> 2014-08-28 23:03 GMT+03:00 Rūdolfs Bundulis <rudolfs.bundulis at gmail.com>:
>
> Hi Klaus,
>>
>> > Was the available monitor hardware limiting you to 16? Because with
>> 720p and the XPDM driver (which is usable with Win7, and I think still the
>> default if you don't enable 3D in the guest additions installer) you should
>> be able to run > with 5x5, too. Needs "only" 226MB for the framebuffers.
>>
>> Well, that is the thing, I don't have the 3D checkbox checked, guest
>> Windows does not allow to enable Aero (so I can assume WDDM is not used?)
>> but the memory bar still warns me when I go above 8 monitors (seems that it
>> always calculates 3 surfaces. Is there any way to check if XPDM or WDDM is
>> actually being used? I could then confirm and fallback to XPDM if that
>> gives me more screens. What I saw in practice is that 7 monitors booted
>> fine in Full HD, when I ran 8 my hint to use 1920x1080 was ignored and all
>> 8 monitors got 1600x1200 resolution, increasing above 10 pushes the
>> resolution down to 1400 x 1050 and so on until when booting with 25 Windows
>> reports only one display at 800x600 (I guess it is simply an overkill for
>> the VRAM). If I could verify if WDDM/XPDM is being used it would become
>> more clear if I can go higher.
>>
>> > Another option might be using 15 or 16bpp in the guest *and* on the
>> host (otherwise color format conversion is necessary, and this kills
>> performance as VirtualBox uses the CPU for that). The GUI again is
>> pessimistic and always ? > expects 24bpp (4 bytes, the packed format again
>> is unbearably slow as it needs conversion), but the virtualizer would work
>> just fine. This would fit into 248MB with 5x5 @1920x1080. Yes, the reduced
>> color resolution sucks, it usually results in heavy color banding.
>>
>> One of the guys involved on our side also suggested this, but we are
>> perofming live video encoding from the framebuffer, 32bpp is great since
>> that can be fed directly to the encoder, anything else will have to be
>> repacked which would not be feasable. Not sure, but since Xubuntu ran
>> really slow, I have a theory that the offscreen surfaces could actually be
>> very useful, since if X11 syncs every draw with the primary surface and
>> locks it, and my software also needs to lock the surface for to at least
>> copy the data, this could be the reason why Xubuntu performs poorly.
>>
>> > Oh sure, we know that VirtualBox can do amazing things (in some areas
>> going far beyond what any virtualizer out there can do), and often shows
>> its great scalability in setups which are a little outside the norm :)
>>
>> Yeah, I am really impressed, when I started my PhD work I was a lot in
>> the dark, wanted to write virtual video card drivers etc., but this is
>> flexible scalable and great, of course if the VRAM limit can be broken.
>> Well I'll lurk around the sources and try to get a grasp of the VRAM
>> things, maybe it is possible to do something there. Thanks a lot for all
>> the input.
>>
>>
>> 2014-08-28 22:12 GMT+03:00 Klaus Espenlaub <klaus.espenlaub at oracle.com>:
>>
>> Rūdolfs,
>>>
>>>
>>> On 28.08.2014 18:15, Rūdolfs Bundulis wrote:
>>>
>>>> Hi Klaus,
>>>>
>>>> I'll mail directly to you this time, since this is not regarding the
>>>> original issue.
>>>>
>>>
>>> Actually if you'd stay on the list then you'd have a chance of getting
>>> more than one team member's knowledge... I'm not really a graphics expert.
>>>
>>>
>>> I ran some tests today, and it seems that at least on
>>>> Windows 7 16 monitors on 1280x720 (720p) work fine. Using our software I
>>>> streamed that to a 4x4 22" monitor wall and that looked really
>>>> impressive.
>>>>
>>>
>>> Was the available monitor hardware limiting you to 16? Because with 720p
>>> and the XPDM driver (which is usable with Win7, and I think still the
>>> default if you don't enable 3D in the guest additions installer) you should
>>> be able to run with 5x5, too. Needs "only" 226MB for the framebuffers.
>>>
>>> Another option might be using 15 or 16bpp in the guest *and* on the host
>>> (otherwise color format conversion is necessary, and this kills performance
>>> as VirtualBox uses the CPU for that). The GUI again is pessimistic and
>>> always expects 24bpp (4 bytes, the packed format again is unbearably slow
>>> as it needs conversion), but the virtualizer would work just fine. This
>>> would fit into 248MB with 5x5 @1920x1080. Yes, the reduced color resolution
>>> sucks, it usually results in heavy color banding.
>>>
>>>
>>> Also tried Xubuntu 14.04 on same configuration but for
>>>> somewhat reason (X11) it was lagging terribly. The question that arose
>>>> was, could you at least provide some base info (as far as it does not
>>>> take too much of your time) what needs to be patched to increase the
>>>> VRAM size?
>>>>
>>>
>>> The easy part is VGA_VRAM_MAX in src/VBox/Devices/Graphics/DevVGA.h and
>>> VRAMSize in src/VBox/Main/xml/VirtualBox-settings.xsd. Not sure if
>>> there are a few more "256 MB" definitions somewhere.
>>>
>>> I bet you'll run into trouble with PCI resource allocation (in our case
>>> done in the code before the VM starts, not in the BIOS like with
>>> conventional PCs), because the bigger area will not fit into the PCI hole
>>> (which is actually normal, I think real systems start with a partial
>>> mapping of the VRAM there, and the graphics driver then relocates it to a
>>> free area past 4GB, at least with 64 bit OSes which can deal properly with
>>> the then necessary 64 bit PCI resources).
>>>
>>> Similarly I guess the BIOS e820 memory map will most likely be broken.
>>>
>>> Many real graphics cards can work with a partially mapped VRAM, giving
>>> access only to 256MB at a time. This would need big changes to our virtual
>>> graphics card and the guest additions driver, but would minimize the need
>>> to change other places.
>>>
>>>
>>> Our research time consists of quite skilled developers so if
>>>> it is not a man-year we would be interrested at least to look into it,
>>>> since the 16 at 720p demo was impressive and seems that this technology
>>>> has
>>>> a future, and currently the biggest limitation is the vram limit in
>>>> VirtualBox. Hope I'm not too intrusive, simply we were all quite
>>>> astonished how this leverages the independence from actual hardware in
>>>> display wall construction, so we are all keen to achieve at least a
>>>> 16x1080p implementation.
>>>>
>>>
>>> Oh sure, we know that VirtualBox can do amazing things (in some areas
>>> going far beyond what any virtualizer out there can do), and often shows
>>> its great scalability in setups which are a little outside the norm :)
>>>
>>> We added support for 64 screens in the days when no one could afford a
>>> full HD screen, and actually the majority of users had only 1024x768, and
>>> users were willing to use 16bpp... it blew the mind of quite a few users
>>> that they could hook up a collection of RDP clients, each providing a
>>> couple of monitors, and get a big video wall this way.
>>>
>>> Regards,
>>> Klaus
>>>
>>>
>>>
>>>> Best Regards,
>>>> Rudolfs Bundulis
>>>>
>>>>
>>>> 2014-08-27 20:11 GMT+03:00 Klaus Espenlaub <klaus.espenlaub at oracle.com
>>>> <mailto:klaus.espenlaub at oracle.com>>:
>>>>
>>>>
>>>> On 27.08.2014 <tel: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 <tel:2014.08.27>. 19:05
>>>> > To: vbox-dev at virtualbox.org <mailto:vbox-dev at virtualbox.org>
>>>>
>>>> > Subject: Re: [vbox-dev] Monitor count limitations
>>>> > Hi Rūdolfs,
>>>> >
>>>> > On 27.08.2014 <tel: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>
>>>> >> <mailto: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>
>>>> <mailto: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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