Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers

[Anthony Liguori]

On 03/31/2011 02:18 PM, Peter Maydell wrote:
> On 31 March 2011 20:01, Anthony Liguori<address@hidden>  wrote:
> > VGA is just another device.  It happens to be that we treat VGA device
> > memory as something that behaves like ram occassionally but that does not
> > make it RAM.
> So, to ask a dumb question, what does make something RAM?

It's a made up concept that we use to make device performance faster.

Basically, RAM should include all of the memory that a reasonable device 
(that we control) would DMA to and has a relatively stable mapping.

> My take on RAM is that RAM is just another device; the only
> difference is that you want to be able to implement fast
> paths that go straight(ish) to target memory; but that's
> an optimisation detail, not something that makes RAM
> conceptually different from other devices...

Right, the trouble is, if you want to treat RAM like any other device, 
you can't get stable mappings to it which is bad for something like 
vhost-net.

Regards,

Anthony Liguori

> -- PMM