Hippo

A Julia Set fractal generated with HIP

• Documentation

Minimal HIP Example

• IMPORTANT: requires at least nim 2.1.9 for gpu usage, and must compile with nim cpp
  • nim 2.1.9 added --cc:nvcc and --cc:hipcc
  • nim cpp is required for both HIP and CUDA.

import hippo

proc addKernel*(a, b: cint; c: ptr[cint]) {.hippoGlobal.} =
  c[] = a + b

var
  c: int32
  dev_c = hippoMalloc(sizeof(int32))
hippoLaunchKernel(addKernel,args = (2,7,dev_c.p))
hippoMemcpy(addr c, dev_c, sizeof(int32), hipMemcpyDeviceToHost)
echo "2 + 7 = ", c

Functions

• There are 3 sets of function prefixes.
• hippo* prefixed functions are friendly nim interfaces for either HIP or CUDA
  • This is the recommended way to use this library, as it is the most nim-like
  • These functions check for errors and raise them as exceptions
• hip* prefixed functions are the raw HIP C++ functions
• cuda* prefixed functions are the raw CUDA C functions

Pragmas

• all pragmas are prefixed with hippo and can be used for hip or cuda to assign attributes like __global__ or __shared__

basic kernel example:

proc add(a,b: int; c: ptr[int]): {.hippoGlobal.} =
  c[] = a + b

Notes

• work in progress!

• very basic kernels work that use block/thread indices

• shared memory works

• there are examples for several different targets in the examples directory.

• building for HIP requires that hipcc is in your PATH

• vector_sum_cuda.nims example .nims for building with hipcc

• vector_sum_hippo.nims example .nims for building with nvcc for cuda

• vector_sum_hip_nvidia.nims example .nims for building with hipcc with the cuda backend

  • tell nim that you want the 'nvcc' compiler settings to get the right arguments, but swap out the compiler executable for hipcc
  • you might also need to have HIP_PLATFORM=nvidia set in your environment

• vector_sum_cpu.nims example .nims for building with the HIP-CPU backend (no hipcc required)

• HIP-CPU is supported with the -d:HippoRuntime=HIP_CPU flag

  • note: you need to pull the HIP-CPU git submodule to use this feature
  • does not require hipcc. works with gcc.
  • you can write kernels and test them on cpu with echos and breakpoints and everything!

• hippo requires that you use cpp. it will not work with c

  • nim cpp -r tests/hip/vector_sum.nim
  • The HIP Runtime is a C++ library, and so is the CUDA Runtime. As such, we can't do anything about this.
  • You can make separate projects for the C and C++ parts and link them together. (I have not tested this yet, would love examples if you do this!)

Motivation

• I want GPU compute (HIP / CUDA) to be a first-class citizen in Nim.

• This library is built around using HIP, which supports compiling for both AMD and NVIDIA GPUs.

  • for CUDA, hipcc is basically a wrapper around nvcc.

• examples for each platform can be found in the examples directory

  • assuming the hipcc compiler is in your PATH, you can run the example with nim cpp -r vector_sum.nim

Compiling

• by default, hipcc will build for the GPU detected in your system.

• If you need to build for various GPUs, you can use --passC:"--offload-arch=gfx1100" to specify the GPU target

  • for example, to build for a 7900 xtx, you would use --passC:"--offload-arch=gfx1100"
  • for a radeon w7500, you would use --passC:"--offload-arch=gfx1102"
  • for a geforce 1650 ti, you would use --passC:"--gpu-architecture=sm_75"
    • You also have to set the HIP_PLATFORM=nvidia environment variable to build for nvidia GPUs if you don't have an nvidia GPU in your system
    • hipcc will pick nvcc by default if you have nvcc but do not have the amd rocm stack installed

• If you want to build for CPU with -d:"HippoRuntime:HIP_CPU", you must have intel tbb libraries installed. yum install -y tbb-devel

Required flags for HIP

• You must compile with nim cpp for c++
• Please refer to the examples for the nim compiler settings needed for each target

Optional flags

• -d:HippoRuntime=HIP (default) (requires hipcc)
  • If you want to build HIP for nvidia, you might need to set the environment variable HIP_PLATFORM=nvidia as well
• -d:HippoRuntime=HIP_CPU for cpu-only usage (does not require hipcc)
  • you must pull the HIP-CPU submodule to use this feature
• -d:HippoRuntime=CUDA (requires nvcc)

Testing

• nimble test to run CPU-only test with HIP_CPU
  • This is what is currently ran on Github CI
• nimble test_amd to compile with hipcc and run on your AMD GPU
• nimble test_cuda to compile with nvcc and run on your NVIDIA GPU

Feature todo list

• support c++ attributes like __global__, __device__
• support kernel execution syntax <<<1,1>>> somehow
• figure out how to handle built-ins like block/thread indices
• Add a compiler option to use HIP-CPU to run HIP code on the CPU
  • will be useful for debugging and testing
  • also useful for running on systems without a GPU
• helper functions to make hip/cuda calls more nim-y
• setup automated testing build for HIP
• setup automated testing with hip-cpu
• support __shared__ w/ a dot product test
• add pictures to project
• Ensure that every example from the book "CUDA by Example" can be run with this library
  • chapter 4 vector + julia set
  • chapter 5 shared memory + thread syncing dot product
  • chapter 6 constant memory + events
  • chapter 7 texture memory (this API changed in recent cuda, might skip)
  • chapter 8 graphics interoperability with boxy
  • chapter 9 atomics
  • chapter 10 streams
  • chapter 11 multi-gpu
  • Advanced Atomics
• setup CI runners for both nvidia & amd GPUs for testing binaries

Stretch goals

• Test with chipStar verify it can run with openCL
• Figure out some way to get this to work with WEBGPU