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Re: [libvirt] [PATCH] qemu: Support ram bar size for qxl devices



> On Thu, Jan 17, 2013 at 09:35:22PM +0200, Alon Levy wrote:
> > Adds a qxl-ram attribute globaly to the video.model element, that
> > changes
> > the resulting qemu command line only if video.type == "qxl".
> > 
> > That attribute gets a default value of 64*1024 only if model.type
> > is
> > "qxl". In effect not changing any xml or argv for non qxl devices.
> > 
> > For qxl devices a new property is set:
> > -global qxl-vga.ram_size=<ram>*1024
> > or
> > -global qxl.ram_size=<ram>*1024
> > 
> > For the main and secondary qxl devices respectively.
> > 
> > The default for the qxl ram bar is the same as the default for the
> > qxl
> > vram bar, 64*1024.
> > ---
> > I've added a qxl-ram attribute. There is no precedent for adding am
> > attribute
> > prefixed like this, so I'm open for any other suggestion on how to
> > do it.
> 
> What is the difference between this new RAM size and what we
> currently
> set for ram size.  That will influence how we pick a good name, ie
> one with any qxl prefix, which is not something we can use.

Answering you, Eric and Michal about the difference / name (I'll do a v2 for Eric's comments anyway):

vram is the current choice for the across the board attribute, and it is used for qxl devices to determine the size of the *second* bar for a qxl device, the surfaces bar. But there is no attribute to determine the size of the first bar. And it isn't good enough to say "use some deterministic connection  between the two, like equality", because you may want to have them with different sizes and we don't yet know what the policy is going to be, for multiple reasons, one of them being that they will effect performance differently, another that seabios doesn't allow setting both to the size we want because of some limitations (512MB seabios PCI allocation hole for pre q35 and for non 64 bit guests).

So I need to add a new attribute. Eric's RNG shows how to limit the new attribute to qxl only by RNG instead of code, which I am glad to know and I'll use. The name can be changed, I wanted to make it abundantly clear to any xml user that this is qxl only right now, but I can change it to just "ram" if you don't think it is confusing (I do).

> 
> Daniel
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