Re: [Qemu-devel] [PATCH] opengl rendering in the sdl window

[Samuel Thibault]

Paul Brook, le Sun 07 Sep 2008 16:03:30 +0100, a écrit :
> On Sunday 07 September 2008, Samuel Thibault wrote:
> > Paul Brook, le Sun 07 Sep 2008 15:36:51 +0100, a écrit :
> > > > Ideally, once switched to fullscreen you could just let the guest
> > > > directly write to the actual video memory (particularly interesting for
> > > > Xen and KVM).
> > >
> > > You really don't want to have the guest writing directly to host video
> > > ram. Video ram tends to be high-latency, so you want to write to regular
> > > memory, then use a wide block transfer or DMA to copy to video ram.
> >
> > How often?  
> 
> You probably want to sync the updates to the vertical refresh. Updating more 
> often than that is pointless.

Sure.

> > Which part(s) of the framebuffer? 
> 
> Whichever parts have changed.

Sure, how do you detect that?
The previous Xen memcmp method was eating 10% cpu for a 30Hz refresh,
just for the memcmp.  Now it uses the pagetable dirty bits and after
some idleness, trapping, but having the guest just write to actual
video memory (when it _has_ to be shown on the screen anyway) seems the
fastest way.

Samuel