EXA classic problem with Xv

Maarten Maathuis madman2003 at gmail.com
Thu Jun 10 12:16:44 PDT 2010

On Thu, Jun 10, 2010 at 8:56 PM, Corbin Simpson
<mostawesomedude at gmail.com> wrote:
> 2010/6/10 Yves De Muyter <yves at alfavisio.be>:
>> Is there any documentation available about the differences between
>> exa_mixed and exa_driver ? Is exa_driver like complete handover of
>> pixmap migration to the driver ?
> The three flavors:
> ~ Classic. EXA handles offscreen pixmaps itself. Simple, except when it breaks.
> ~ Driver. EXA lets the driver control pixmap allocation and placement.
> Great if you have a memory manager.
> ~ Mixed. Like driver, but certain things have been tweaked to optimize
> certain kinds of acceleration in a way that was never really explained
> to me.

mixed has parts from classic that avoid touching driver pixmaps
directly for fallbacks (vram is slow to access from the cpu). Xorg's
unique access patterns are not well suited to modern gpu's IMO. That's
why mixed was made. Mixed would be useless if our world was 100% gpu
accelerated, but unfortunately it's not.

For mixed you can also fail prepare access on the frontbuffer, which
allows you to make a driver that doesn't allow mapping of vram,
provided you have a UTS and DFS hook that always works.

For igp'ish hardware without dedicated memory and a decent memory
manager, exa driver is preferred because it's the simplest driver mode
and avoids overhead that is unneeded for such hardware.

> To go from driver to mixed is pretty simple; here's an example commit:
> http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/commit/?id=577ff3ce922e457cc32f80d4365cb1da81552e72
> ~ C.
> --
> When the facts change, I change my mind. What do you do, sir? ~ Keynes
> Corbin Simpson
> <MostAwesomeDude at gmail.com>
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