[Mesa-dev] [Patch] Sharing flags should disable tiling

[Kristian Høgsberg]

On Mon, Aug 12, 2013 at 3:05 PM, Marek Olšák <maraeo at gmail.com> wrote:
> On Mon, Aug 12, 2013 at 11:36 PM, Stéphane Marchesin
> <stephane.marchesin at gmail.com> wrote:
>>> Other than hybrid systems (of which
>>> there are none with i915 graphics), is there any case where
>>> __DRI_IMAGE_USE_SHARE can occur?
>>
>> You could do interesting things like cross-process sharing with it. I
>> think it's worth doing it, no matter what. It's easy to pick up now,
>> and hard to fix up later.
>
> Cross-process sharing is mandatory already and exposed via
> resource_from_handle and resource_get_handle. I don't think this is
> useful for cross-process sharing anyway, because it disables tiling.

No, we need a different flag for this.  I can't speak to the gallium
flag, but the __DRI_IMAGE_USE_SHARE flag is use for same-gpu cross
process sharing under wayland, either using GEM names or Prime fd
passing.  We can't drop tiling in this case, there's an obvious
performance penalty.  We need a flag to indicate that a buffer will be
used on multiple GPUs.  The next level up in the stack
(src/egl/drivers/dri2/platform_wayland.c in case of Wayland) needs to
know whether or not a buffer will be used in this way and pass the
flag when applicable.

Kristian