Gallium3D OpenCL GSoC Near-Final Status Update

[plonoma]

Hello,

Here are more details about the status of Clover:

• The API is complete, that means that any application can now use Clover and will not fail due to missing or unimplemented symbols.
• The implementation in itself is complete: there are no stubs, and all the API actually does something.
• The interesting part: Clover can launch native kernels (Phoronix spoke about that two months ago), and compiled kernels. So, it is really feature-complete.
• The only thing missing are built-ins functions. It means that even if we can create memory objects, images, events, command queues and all the OpenCL objects, and that we can compile and launch OpenCL C kernels, these kernel cannot yet use functions like clamp(), smooth(), etc.
• The most complex built-ins are implemented though, like image reading and writing, and barrier() (a built-in that will be described in detail in the documentation as it uses things like POSIX contexts (man setcontext)).

I'll write the documentation in the following days (I already begun). It will be in Doxygen format, and I was pleased yesterday to see that Doxygen is now able to produce exceptionally good and beautiful documentation, in regards of what it produced one or two years ago. Then, I'll rework some part of the image functions (they are currently tied to the x86 architecture using SSE2, I will reimplement them in a more architecture-neutral way).

The documentation will be available in the source code and also on my people.freedesktop.org page, so anybody will be able to view it.

Please add what version of OpenCL is implemented on the main page of your documentation. The references used from khronos to build this would be very informative.

[bridgman]

does this mean that AMD has already writtern the code we need to make it run on GPUs ????

Sort of... we have an LLVM backend which generates AMD IL, then we run AMD IL through the proprietary shader compiler to generate hardware ISA, ie LLVM IR => AMD IL => ISA. We are looking at the LLVM bits from the proprietary stack to see what can be opened and re-used.

Zack's statement assumes we can open up the proprietary shader compiler, which is not an option today. We are looking at options for the open stack, and with some luck we can discuss at XDC.

[89c51]

i was googling around to try to get a better idea on the discussion happening here and i found this quote by Zack Rusin:

In the case of AMD it's even sadder because the crucial code that we need for OpenCL right now is OpenCL C -> TGSI LLVM backend which AMD already does for their IL. Some poor schmuck will have to sit down and write more/less the same code."

does this mean that AMD has already writtern the code we need to make it run on GPUs ????

[steckdenis]

Hello,

Just to say that the documentation I'm writing is available on http://people.freedesktop.org/~steck...ver/index.html . Sorry for the bad English (it is already a bit special in short messages, so I don't imagine in whole documentation pages), comments and corrections welcome.

This documentation will be expanded in the following days. I recommend to clone the Clover's git repository (http://cgit.freedesktop.org/~steckdenis/clover) and to build the documentation yourself, as Freedesktop.org uses a very outdated version of Doxygen and Dot. By using a modern distribution, you'll get a way more beautiful documentation (smoothed dot graphs, nicer page layout, logo, etc).

[pingufunkybeat]

So, let me see if I got this right...

Clover implements the complete OpenCL API and can execute OpenCL programs. But at the moment, all of it runs on the CPU, and getting it to actually run on GPUs will be a hitload of work and nobody really knows how it should be done.

And this is due to a few factors:

- the situation regarding IRs in Gallium is muddy: Mesa IR seems to be on the way out, with TGSI being generated directly, but there are attempts to use LLVM too, and GLSL IR is also in the mix
- TGSI is good for graphics (shaders), but is not good for computing, like OpenCL, which is why people are proposing LLVM
- LLVM sucks at graphics

So we're likely looking at (at least) two IRs coexisting: one for shaders, one for OpenCL stuff?

[bridgman]

Here are more details about the status of Clover:
...

Denis, that is some really nice work -- a *very* productive summer.

[Drago]

And another very important thing.
Is this going to be OpenCL 1.0 or 1.1?

1.1 bla,bla

[plonoma]

And another very important thing.
Is this going to be OpenCL 1.0 or 1.1?

[steckdenis]

Hello,

Here are more details about the status of Clover:

• The API is complete, that means that any application can now use Clover and will not fail due to missing or unimplemented symbols.
• The implementation in itself is complete: there are no stubs, and all the API actually does something.
• The interesting part: Clover can launch native kernels (Phoronix spoke about that two months ago), and compiled kernels. So, it is really feature-complete.
• The only thing missing are built-ins functions. It means that even if we can create memory objects, images, events, command queues and all the OpenCL objects, and that we can compile and launch OpenCL C kernels, these kernel cannot yet use functions like clamp(), smooth(), etc.
• The most complex built-ins are implemented though, like image reading and writing, and barrier() (a built-in that will be described in detail in the documentation as it uses things like POSIX contexts (man setcontext)).

I'll write the documentation in the following days (I already begun). It will be in Doxygen format, and I was pleased yesterday to see that Doxygen is now able to produce exceptionally good and beautiful documentation, in regards of what it produced one or two years ago. Then, I'll rework some part of the image functions (they are currently tied to the x86 architecture using SSE2, I will reimplement them in a more architecture-neutral way).

The documentation will be available in the source code and also on my people.freedesktop.org page, so anybody will be able to view it.

[Plombo]

Ha, yes, understatement of the year. I only meant to say that while we can likely expect further improvements on the code here, i don't think you can expect this developer to finish coding a full GPU implementation. That's going to take at LEAST another GSoC, and possibly more. I wasn't aware of what all needed to be done - modifying Gallium drivers to accept LLVM directly seems like a good idea, but that's probably multiple GSoC's right there just for that part.

And wasn't the developers consensus largely that they weren't that hot about LLVM? IIRC, it sounded like the least controversial option to drop TGSI was to replace it with the GLSL IR, and some devs in particular were pretty anti-LLVM. I have no idea if that supports the sort of operations it would need to or not.

Well, compute != graphics. The developer consensus on LLVM is that it's not well-suited for shaders, i.e. graphics. Compute is a different matter.

If we're lucky, we can get Gallium driver developers to add LLVM IR support to their drivers, if someone comes up with a good way to code-generate for GPUs using LLVM. But I would guess that the LunarGLASS developers have already figured that part out. Or at least, I think they've figured out a way to code generate for targets that require structured control flow. I think they said a few months ago that they had gotten it working when targeting Mesa IR, which requires structured control flow like GPUs. So maybe some of their work can be adapted to Clover.