[Mesa-dev] Request for support of GL_AMD_pinned_memory and GL_ARB_buffer_storage extensions

[Marek Olšák]

Yes, GL_ARB_buffer_storage is being worked on. We'll support it on all
Radeon cards R300 and up.

Anyway, GL_STREAM_DRAW should give you the same behavior as
GL_CLIENT_STORAGE_BIT on open source Radeon drivers.

Marek

On Sun, Nov 24, 2013 at 1:19 PM, Tony Wasserka <neobrainx at googlemail.com> wrote:
> Hello everyone,
> I was told on IRC that my question would get most attention around here - so
> bear with me if this is the wrong place to ask
>
> I'm one of the developers of the GC/Wii emulator Dolphin. We recently
> rewrote our OpenGL renderer to use modern OpenGL 3 features, however one
> thing that we stumbled upon are the lack of efficient (vertex/index) buffer
> data streaming mechanisms in OpenGL. Basically, most of our vertex data is
> used once and never again after that (we have to do this for accurate
> emulation) - so all vertex data gets streamed into one huge ring buffer (and
> analogously for index data, which uses its own huge ring buffer). For buffer
> streaming, we have multiple code paths using a combination of
> glMapBufferRange, glBufferSubData, fences and buffer orphaning, yet none of
> these come anywhere close to the performance of (legacy) rendering from a
> vertex array stored in RAM.
>
> There are two OpenGL extensions which greatly help us in this situation:
> AMD's pinned memory [1], and buffer storage[2] in GL 4.4. We currently have
> no buffer storage code path, but usage of pinned memory gave us a speedup of
> up to 60% under heavy workloads when working with AMD's Catalyst driver
> under Windows. We expect the same speedup when using buffer storage
> (specifically we need CLIENT_STORAGE_BIT, if I recall correctly).
>
> So the natural question that arises is: Is either of these two extensions
> going to be supported in mesa anytime soon or is it of lower priority than
> other extensions? Also, is the pinned memory extension AMD hardware specific
> or would it be possible to support it for other hardware, too? I'm not sure
> if buffer storage (being a GL 4.4 extension, and I read that it might
> actually depend on some other GL 4.3 extension) is possible to implement on
> older hardware, yet it would be very useful for us to have efficient
> streaming methods for old GPUs, too.
>
> I hope this mail doesn't sound too commanding or anything, it's just
> supposed to be a friendly question on improving the emulator experience for
> our user base
> Thanks in advance!
>
> Best regards,
> Tony
>
> [1] http://www.opengl.org/registry/specs/AMD/pinned_memory.txt
> [2] http://www.opengl.org/registry/specs/ARB/buffer_storage.txt
>
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