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Re: [libvirt] [PATCH v2 0/4] use the 'vram' attribute for QEMU video devices

On 11/14/2014 04:00 PM, Gerd Hoffmann wrote:

The 'vgamem_mb' parameter for QXL sets the VGA framebuffer size, but the VGA
mode in QXL is used only as fallback if the OS doesn't have any QXL drivers
or before the drivers are loaded. The VGA framebuffer is part of the first ram
for QXL and for that we have 'ram' attribute. The rest of the first ram is
memory for rendering commands and it's data. Default VGA framebuffer size is
8MB which is sufficient.

It isn't that simple.   The vga framebuffer can be used as as video
memory in non-vga mode too.  Guest driver can choose whenever it uses
the vga framebuffer or vram bar.

Traditional behavior is to use the vga framebuffer, in fact very old qxl
device revisions don't have a vram pci bar in the first place.  Because
of that vgamem_mb should be configurable on qxl too.


Hi Gerd,

I thought that it isn't that simple. Thanks for the clarification. The
goal of those patches is to have only one 'vram' attribute in libvirt's
XML and it should be used to set the size of video memory for different
video devices for different hypervisors. It's simple for all QEMU video
devices except the QXL where you can set 3 different parameters.

That's probably good point to also introduce a way to set the]
'vgamem_mb' for QXL.

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