Ramon van Handel wrote:
> > Using synchronous updates instead of async ones may be
> > even slower: there can be a *lot* of accesses to the video
> > memory, and causing a full VM switch for every byte written
> > might well be much slower than just reading the whole
> > thing say 50 times a second.
>
> Uh... hang on. I never mentioned this. What are you
> referring to, exactly ? I said
Ah, I seem to have mis-read what you were saying. Sorry.
[snip mapping host frame buffer]
I wasn't thinking of this at all; at the current stage, IMO we
shouldn't touch the real host hardware directly in any way.
I was just talking about possible ways to implement emulated VGA
hardware, either by asynchronous means (read out the guest frame
buffer periodically) or by synchronous means (trap guest access
to the frame buffer, like we trap I/O access -- this is how Bochs
does it AFAIK).
> (2) that you can use the dirty bit to check, whether
> the guest wrote to the framebuffer memory.
> There's no reason that this should imply mapping
> the FB read-only... to the contrary, it avoids it.
If you do in fact map the host frame buffer, you don't even *need*
to check whether it was modified -- it is already displayed. You
could use this information to help the asynch frame buffer emulation,
however, so that you can skip updating the video display if the guest
didn't touch the (emulated) guest frame buffer during the last tick.
Bye,
Ulrich
--
Ulrich Weigand,
IMMD 1, Universitaet Erlangen-Nuernberg,
Martensstr. 3, D-91058 Erlangen, Phone: +49 9131 85-27688
