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Re: [Xen-devel] libxl videoram for cirrus graphics

On Tue, 17 Sep 2013, Ian Campbell wrote:
> On Tue, 2013-09-17 at 12:54 +0000, Rob Hoes wrote:
> > Hi,
> > 
> > The videoram setting in xl config files is documented as follows:
> > 
> > "
> > videoram=MBYTES
> > 
> >     Sets the amount of RAM which the emulated video card will contain,
> > which in turn limits the resolutions and bit depths which will be
> > available. The default amount of video ram for stdvga is 8MB which is
> > sufficient for e.g. 1600x1200 at 32bpp and videoram option is
> > currently working only when using the qemu-xen-traditional
> > device-model.
> > 
> >     When using the emulated Cirrus graphics card (vga="cirrus") the
> > amount of video ram is fixed at 4MB which is sufficient for 1024x768
> > at 32 bpp and videoram option is currently working only when using the
> > upstream qemu-xen device-model.
> > "
> > 
> > XenServer also uses a default of 4MB video ram for cirrus graphics.
> > 
> > However, when I use xl to create a VM with cirrus graphics, I get 8MB
> > of video RAM by default. Moreover, setting it to videoram=4 in the
> > config file leads to complaints from libxl:
> > 
> >     libxl_create.c:228:libxl__domain_build_info_setdefault: videoram must 
> > be at least 8 mb
> > 
> > Is there a bug in the logic in libxl_create.c?
> Either the docs of the code or both would seem to be wrong. Since you
> say you happily use 4MB in XenServer I guess it is both?
> I noticed that the docs also say the amount is fixed, but that's not
> what the code implements either..
> I'm not really sure who, if anyone, might know definitively what is
> going on here. Stefano has some involvement in this video mem stuff once
> upon a time and Ian is the qemu-trad maintainer, so I've CCdthem
> both ;-)

AFAICT we always had 8 mb for Cirrus in libxl. I am not really sure
where this discrepancy between the docs and the code comes from.

I think that if 4mb actually works fine with different guests OSes then
we should allow it.

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