[PATCH 0/4] fb support for 8bpp bitmaps

Michel Dänzer michel at daenzer.net
Wed Jan 15 20:08:12 PST 2014

On Mit, 2014-01-15 at 19:43 -0800, Keith Packard wrote:
> Michel Dänzer <michel at daenzer.net> writes:
> > But why are you putting so much effort into trying to share storage
> > between GPU and CPU for bitmaps, given that SNA has apparently proved
> > such sharing is not beneficial overall even on Intel GPUs?
> Did you look at how 'hard' getting GPU-acceleratable depth-1
> pixmaps was?

That doesn't cover making GPU texture memory directly accessible in
Mesa, glamor etc.

> > It seems more useful to spend effort on maintaining separate persistent
> > CPU storage for software fallbacks, which has proven effective in EXA
> > and SNA.
> That's a huge waste of time if your goal is to never touch pixmaps with
> the CPU at all. The only reason you should ever be migrating pixmaps is
> if you have a non-UMA machine and simply run out of GPU-accessible
> storage.
> "software fallbacks" is just another name for "failure"...

I totally agree with that, but the experience with EXA and SNA (and
glamor) has shown that it'll take a *lot* of effort to eliminate them
completely. And as long as there is even just a single software
rendering path, there's bound to be some app out there hitting it and
performing very badly without an appropriate fallback mechanism.

Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer
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