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

[Avi Kivity]

On 05/19/2011 04:49 PM, Anthony Liguori wrote:
> On 05/19/2011 08:30 AM, Avi Kivity wrote:
> > On 05/19/2011 04:26 PM, Jan Kiszka wrote:
> > > On 2011-05-19 15:07, Avi Kivity wrote:
>
> > > And when introducing hierarchical registration, we will have to go
> > > through all of this once again. Plus the API may have to be changed
> > > again if it does not fulfill all requirements of the hierarchical 
> > > region
> > > management. And we have no proof that it allows an efficient core
> > > implementation.
> >
> > This API *is* hierarchical registration. v2 will (hopefully) prove that
> > it can be done efficiently.
>
> We also need hierarchical dispatch.  Priorities are just a weak 
> attempt to emulate hierarchical dispatch but I don't think there's an 
> improvement over a single dispatch table.
>
> Hierarchical dispatch is simpler.  You just need a simple list at each 
> bus.

The API itself says nothing about whether the hierarchy is evaluated at 
run-time or registration time.  We could easily have the implementation 
walk the memory hierarchy to dispatch an mmio.

However, RAM cannot be dispatched this way (we need to resolve which 
ranges are RAM when the regions are registered, not accessed) so a data 
structure that contains all of the information is mandatory.

Since the first implementation will use the existing 
cpu_physical_register_memory() API as a back-end, we'll end up with a 
flattened dispatch model (which I think is the right thing anyway).

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