Re: [Qemu-devel] [RFC] Memory API

[Gleb Natapov]

On Sun, May 22, 2011 at 10:37:48AM +0300, Avi Kivity wrote:
> On 05/20/2011 02:57 PM, Gleb Natapov wrote:
> >On Fri, May 20, 2011 at 11:59:58AM +0300, Avi Kivity wrote:
> >>  On 05/19/2011 07:27 PM, Gleb Natapov wrote:
> >>  >>   Think of how a window manager folds windows with priorities onto a
> >>  >>   flat framebuffer.
> >>  >>
> >>  >>   You do a depth-first walk of the tree.  For each child list, you
> >>  >>   iterate it from the lowest to highest priority, allowing later
> >>  >>   subregions override earlier subregions.
> >>  >>
> >>  >I do not think that window manager is a good analogy. Window can
> >>  >overlap with only its siblings. In our memory tree each final node may
> >>  >overlap with any other node in the tree.
> >>  >
> >>
> >>  Transparent windows.
> >>
> >No, still not that. Think about child windows that resides outside of its
> >parent windows on screen. In our memory region terms think about PCI BAR
> >is registered to overlap with RAM at address 0x1000 for instance. PCI
> >BAR memory region and RAM memory region are on very different branches
> >of the global tree.
> 
> Right.  But what's the problem with that?
> 
None, unless you want to make PCI BAR visible at address 0x1000 (like what
will happen today) the case above. 

> Which one takes precedence is determined by the priorities of the
> RAM subregion vs. the PCI bus subregion.
> 
Yes, and that is why PCI subsystem or platform code can't directly uses
memory API to register PCI memory region/RAM memory region respectively,
because they wouldn't know what priorities to specify. Only chipset code
knows, so the RAM/PCI memory registration should go through chipset
code, but even chipset code doesn't know everything. It knows nothing
about cpu local memory regions for instance, so all registrations should
go through system bus in the end. Is this how API suppose to be used?

--
                        Gleb.