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VeriGPU: GPU in Verilog loosely based on RISC-V ISA

101 points by btdmaster 4y ago

atq2119 4y ago
From the planning document: > Branching: Done > Single instruction multiple thread (SIMT): Planned I guess we should be supportive, and it is impressive how far they got on the software side, but boy, is the author in for a surprise.
mrintellectual 4y ago
Even as an ML-focused graphics-less GPU, this is great. If this can be prototyped on an FPGA, it would be even better. Using block RAM for shared memory and built-in PCIe and DDR IP blocks should help speed things up considerably. It unfortunately wouldn't be very cost-effective for training ML models, but it would take things a step closer to actual tape-out (if some organization has the $$$ for it).
terafo 4y ago
I'm interested whether it would be a good idea to implement a Vulkan driver for such GPU via emulating TMUs and ROPs in software, and it might not even matter that much since modern rendering pipelines are more and more compute reliant anyways(UE5 Nanite barely uses hardware rasterizers, latest idTech uses software rasterization as well). The only problem I see lies is with raytracing since it is pretty reliant on fixed function units.
- sylware 4y ago
  hu? You mean that the latest idTech engine is not using the fixed-function 3D pipeline at all, namely full compute (no vertex/fragment shaders)? Still using the texture sampling units?
  - Jasper_ 4y ago
    No, it still uses triangles. That seems to be a misunderstanding of how they do their clusters: They switched to a software rasterizer for drawing light volumes and decals into the clustered light buffer, meaning it's now a scatter rather than a gather (parallelized over lights, rather than tiles). This is pretty standard, but it's limited to those low res cluster info buffers, and is only rasterizing a handful of triangles per light.
- Jasper_ 4y ago
  Every 10 years, someone will reinvent Larabee.
avianes 4y ago
I'm not really optimistic about the hardware and the tape-out goal. The author seems to have a very basic knowledge about it. For instance, the int multiplier design is overengineered, very naive and far from state of the art (no pipeline, no adder compressor). I would suggest the author to check wallace tree multiplier. But at this stage it would be preferable to use the native verilog multiply or a DSP macro to target FPGA for prototyping, and to focus the SIMT architecture and the pipelining. Arithmetic unit design is a science in its own. However it's a beautiful project!
Sirened 4y ago
Neat! Looks like it's very much in its early stages (no concurrent execution/threads yet) but it's so great to see FOSS digital design work in an industry dominated by huge players
tux3 4y ago
Worth noting this is targeting ML applications, so I don't think you'll be able to display even a text console with it for the foreseeable future. But I love that this is even in the realm of possibilities! There's no reason we couldn't, in principle, have a small open-source GPU taping out on the free Skywater shuttle, and I am here for it!
- milkey_mouse 4y ago
  It's funny that we've gotten to the point that a "graphics-less GPU" is actually useful. Perhaps they should call it something else...
  - dahart 4y ago
    I feel like the name’s been funny for a decade and a half, and a new name might be coming, but GPU has been pretty synonymous with massively parallel vector/SIMD processor for a long time, right? Most still have some dedicated graphics functionality, but people have also been using them for high performance headless compute for quite a while. I certainly prefer just GPU over GPGPU. It seems hard to change though, and might be confusing to call it a vector processor, considering CPUs have vector/SIMD support. So what would be a better name?
    - my123 4y ago
      GPUs without graphics support are already a thing. But so far, NVIDIA is staying on the GPU term. For the H100, very minimalistic FF support was picked. Only two TPCs in both the SXM5 and PCIe H100 GPUs are graphics-capable (that is, they can run vertex, geometry, and pixel shaders). And that’s out of: 8 GPCs, 66 TPCs, 2 SMs/TPC, 132 SMs per GPU for an H100 SXM5. Aka just for compatibility.
  - fithisux 4y ago
    GPPU
  - uluyol 4y ago
    Well there are definitely cases where you want to render frames and not view them in real time. For example, rendering the final cut of an animated movie.
yjftsjthsd-h 4y ago
> Internal GPU Core ISA loosely compliant with RISC-V ISA. Where RISC-V conflicts with designing for a GPU setting, we break with RISC-V. Very amateur question: I thought RISC-V added vector extensions so you could use it directly for GPU/TPU chips without having to fragment the ecosystem?
- colejohnson66 4y ago
  The V extension is more akin to the various SIMD extensions of x86 (SSE/AVX) or ARM (NEON) than a GPU system. I’m sure one could make a GPU based on RV-V, but the extension is more GPGPU like than a pixel/shader pipeline.
lizardactivist 4y ago
Very cool, but can someone remind me what "GPU" means again?
- Frenchgeek 4y ago
  Generic Processing Unit, it seems.
- deleted 4y ago
  [deleted]
gnufx 4y ago
Perhaps also see the (OpenPOWER-based) Libre-SOC effort https://libre-soc.org/ https://libre-soc.org/

101 points by btdmaster 4y ago

From the planning document: > Branching: Done > Single instruction multiple thread (SIMT): Planned I guess we should be supportive, and it is impressive how far they got on the software side, but boy, is the author in for a surprise.

mrintellectual 4y ago

Even as an ML-focused graphics-less GPU, this is great. If this can be prototyped on an FPGA, it would be even better. Using block RAM for shared memory and built-in PCIe and DDR IP blocks should help speed things up considerably. It unfortunately wouldn't be very cost-effective for training ML models, but it would take things a step closer to actual tape-out (if some organization has the $$$ for it).

terafo 4y ago

I'm interested whether it would be a good idea to implement a Vulkan driver for such GPU via emulating TMUs and ROPs in software, and it might not even matter that much since modern rendering pipelines are more and more compute reliant anyways(UE5 Nanite barely uses hardware rasterizers, latest idTech uses software rasterization as well). The only problem I see lies is with raytracing since it is pretty reliant on fixed function units.

sylware 4y ago
hu? You mean that the latest idTech engine is not using the fixed-function 3D pipeline at all, namely full compute (no vertex/fragment shaders)? Still using the texture sampling units?
- Jasper_ 4y ago
  No, it still uses triangles. That seems to be a misunderstanding of how they do their clusters: They switched to a software rasterizer for drawing light volumes and decals into the clustered light buffer, meaning it's now a scatter rather than a gather (parallelized over lights, rather than tiles). This is pretty standard, but it's limited to those low res cluster info buffers, and is only rasterizing a handful of triangles per light.
Jasper_ 4y ago
Every 10 years, someone will reinvent Larabee.

avianes 4y ago

I'm not really optimistic about the hardware and the tape-out goal. The author seems to have a very basic knowledge about it. For instance, the int multiplier design is overengineered, very naive and far from state of the art (no pipeline, no adder compressor). I would suggest the author to check wallace tree multiplier. But at this stage it would be preferable to use the native verilog multiply or a DSP macro to target FPGA for prototyping, and to focus the SIMT architecture and the pipelining. Arithmetic unit design is a science in its own. However it's a beautiful project!

Sirened 4y ago

Neat! Looks like it's very much in its early stages (no concurrent execution/threads yet) but it's so great to see FOSS digital design work in an industry dominated by huge players

tux3 4y ago

Worth noting this is targeting ML applications, so I don't think you'll be able to display even a text console with it for the foreseeable future. But I love that this is even in the realm of possibilities! There's no reason we couldn't, in principle, have a small open-source GPU taping out on the free Skywater shuttle, and I am here for it!

milkey_mouse 4y ago
It's funny that we've gotten to the point that a "graphics-less GPU" is actually useful. Perhaps they should call it something else...
- dahart 4y ago
  I feel like the name’s been funny for a decade and a half, and a new name might be coming, but GPU has been pretty synonymous with massively parallel vector/SIMD processor for a long time, right? Most still have some dedicated graphics functionality, but people have also been using them for high performance headless compute for quite a while. I certainly prefer just GPU over GPGPU. It seems hard to change though, and might be confusing to call it a vector processor, considering CPUs have vector/SIMD support. So what would be a better name?
  - my123 4y ago
    GPUs without graphics support are already a thing. But so far, NVIDIA is staying on the GPU term. For the H100, very minimalistic FF support was picked. Only two TPCs in both the SXM5 and PCIe H100 GPUs are graphics-capable (that is, they can run vertex, geometry, and pixel shaders). And that’s out of: 8 GPCs, 66 TPCs, 2 SMs/TPC, 132 SMs per GPU for an H100 SXM5. Aka just for compatibility.
- fithisux 4y ago
  GPPU
- uluyol 4y ago
  Well there are definitely cases where you want to render frames and not view them in real time. For example, rendering the final cut of an animated movie.

yjftsjthsd-h 4y ago

> Internal GPU Core ISA loosely compliant with RISC-V ISA. Where RISC-V conflicts with designing for a GPU setting, we break with RISC-V. Very amateur question: I thought RISC-V added vector extensions so you could use it directly for GPU/TPU chips without having to fragment the ecosystem?

colejohnson66 4y ago
The V extension is more akin to the various SIMD extensions of x86 (SSE/AVX) or ARM (NEON) than a GPU system. I’m sure one could make a GPU based on RV-V, but the extension is more GPGPU like than a pixel/shader pipeline.

lizardactivist 4y ago

Very cool, but can someone remind me what "GPU" means again?

Frenchgeek 4y ago
Generic Processing Unit, it seems.
deleted 4y ago
[deleted]

gnufx 4y ago

Perhaps also see the (OpenPOWER-based) Libre-SOC effort https://libre-soc.org/ https://libre-soc.org/