CUDA


CUDA is a proprietary parallel computing platform and application programming interface that allows software to use certain types of graphics processing units for accelerated general-purpose processing, significantly broadening their utility in scientific and high-performance computing. CUDA was created by Nvidia starting in 2004 and was officially released in 2007. When it was first introduced, the name was an acronym for Compute Unified Device Architecture, but Nvidia later dropped the common use of the acronym and now rarely expands it.
CUDA is both a software layer that manages data, giving direct access to the GPU and CPU as necessary, and a library of APIs that enable parallel computation for various needs. In addition to drivers and runtime kernels, the CUDA platform includes compilers, libraries and developer tools to help programmers accelerate their applications.
CUDA is written in the C programming language but is designed to work with a wide array of other programming languages including C++, Fortran, Python and Julia. This accessibility makes it easier for specialists in parallel programming to use GPU resources, in contrast to prior APIs like Direct3D and OpenGL, which require advanced skills in graphics programming. CUDA-powered GPUs also support programming frameworks such as OpenMP, OpenACC and OpenCL.

Background

The graphics processing unit, as a specialized computer processor, addresses the demands of real-time high-resolution 3D graphics compute-intensive tasks. By 2012, GPUs had evolved into highly parallel multi-core systems allowing efficient manipulation of large blocks of data. This design is more effective than general-purpose central processing unit for algorithms in situations where processing large blocks of data is done in parallel, such as:
The origins of CUDA trace to the early 2000s, when Ian Buck, a computer science Ph.D. student at Stanford University, began experimenting with using GPUs for purposes beyond rendering graphics. Buck had first become interested in GPUs during his undergraduate studies at Princeton University, initially through video gaming. After graduation, he interned at Nvidia, gaining deeper exposure to GPU architecture. At Stanford, he built an 8K gaming rig using 32 GeForce graphics cards, originally to push the limits of graphics performance in games like Quake and Doom. However, his interests shifted toward exploring the potential of GPUs for general-purpose parallel computing.
To that end, Buck developed Brook, a programming language designed to enable general-purpose computing on GPUs. His work attracted support from both Nvidia and the Defense Advanced Research Projects Agency. In 2004, Nvidia hired Buck and paired him with John Nickolls, the company's director of architecture for GPU computing. Together, they began transforming Brook into what would become CUDA. CUDA was officially released by Nvidia in 2007.
Under the leadership of Nvidia CEO Jensen Huang, CUDA became central to the company's strategy of positioning GPUs as versatile hardware for scientific applications. By 2015, CUDA's development increasingly focused on accelerating machine learning and artificial neural network workloads.

Ontology

The following table offers a non-exact description for the ontology of the CUDA framework.
memory
memory computation
computation
computation
RAMnon-CUDA variableshostprogramone routine call
VRAM,
GPU L2 cache		global, const, texturedevicegridsimultaneous call of the same subroutine on many processors
GPU L1 cachelocal, sharedSM blockindividual subroutine call
warp = 32 threadsSIMD instructions
GPU L0 cache,
register		thread analogous to individual scalar ops within a vector op

Programming abilities

The CUDA platform is accessible to software developers through CUDA-accelerated libraries, compiler directives such as OpenACC, and extensions to industry-standard programming languages including C, C++, Fortran and Python. C/C++ programmers can use 'CUDA C/C++', compiled to PTX with nvcc or by clang itself. Fortran programmers can use 'CUDA Fortran', compiled with the PGI CUDA Fortran compiler from The Portland Group. Python programmers can use the cuPyNumeric library to accelerate applications on Nvidia GPUs.
In addition to libraries, compiler directives, CUDA C/C++ and CUDA Fortran, the CUDA platform supports other computational interfaces, including the Khronos Group's OpenCL, Microsoft's DirectCompute, OpenGL Compute Shader and C++ AMP. Third party wrappers are also available for Python, Perl, Fortran, Java, Ruby, Lua, Common Lisp, Haskell, R, MATLAB, IDL, Julia, and native support in Mathematica.
In the computer game industry, GPUs are used for graphics rendering, and for game physics calculations ; examples include PhysX and Bullet. CUDA has also been used to accelerate non-graphical applications in computational biology, cryptography and other fields by an order of magnitude or more.
CUDA provides both a low level API and a higher level API. The initial CUDA SDK was made public on 15 February 2007, for Microsoft Windows and Linux. Mac OS X support was later added in version 2.0, which supersedes the beta released February 14, 2008. CUDA works with all Nvidia GPUs from the G8x series onwards, including GeForce, Quadro and the Tesla line. CUDA is compatible with most standard operating systems.
CUDA 8.0 comes with the following libraries :
  • cuBLAS – CUDA Basic Linear Algebra Subroutines library
  • CUDART – CUDA Runtime library
  • cuFFT – CUDA Fast Fourier Transform library
  • cuRAND – CUDA Random Number Generation library
  • cuSOLVER – CUDA based collection of dense and sparse direct solvers
  • cuSPARSE – CUDA Sparse Matrix library
  • NPP – NVIDIA Performance Primitives library
  • nvGRAPH – NVIDIA Graph Analytics library
  • NVML – NVIDIA Management Library
  • NVRTC – NVIDIA Runtime Compilation library for CUDA C++
CUDA 8.0 comes with these other software components:
  • nView – NVIDIA nView Desktop Management Software
  • NVWMI – NVIDIA Enterprise Management Toolkit
  • GameWorks PhysX – is a multi-platform game physics engine
CUDA 9.0–9.2 comes with these other components:
  • CUTLASS 1.0 – custom linear algebra algorithms,
  • NVIDIA Video Decoder was deprecated in CUDA 9.2; it is now available in NVIDIA Video Codec SDK
CUDA 10 comes with these other components:
  • nvJPEG – Hybrid JPEG processing
CUDA 11.0–11.8 comes with these other components:
  • CUB is new one of more supported C++ libraries
  • MIG multi instance GPU support
  • nvJPEG2000 – JPEG 2000 encoder and decoder

    Advantages

CUDA has several advantages over traditional general-purpose computation on GPUs using graphics APIs:
  • Scattered readscode can read from arbitrary addresses in memory
  • Unified virtual memory
  • Unified memory
  • Shared memoryCUDA exposes a fast shared memory region that can be shared among threads. This can be used as a user-managed cache, enabling higher bandwidth than is possible using texture lookups.
  • Faster downloads and readbacks to and from the GPU
  • Full support for integer and bitwise operations, including integer texture lookups

    Limitations

  • Whether for the host computer or the GPU device, all CUDA source code is now processed according to C++ syntax rules. This was not always the case. Earlier versions of CUDA were based on C syntax rules. As with the more general case of compiling C code with a C++ compiler, it is therefore possible that old C-style CUDA source code will either fail to compile or will not behave as originally intended.
  • Interoperability with rendering languages such as OpenGL is one-way, with OpenGL having access to registered CUDA memory but CUDA not having access to OpenGL memory.
  • Copying between host and device memory may incur a performance hit due to system bus bandwidth and latency.
  • Threads should be running in groups of at least 32 for best performance, with total number of threads numbering in the thousands. Branches in the program code do not affect performance significantly, provided that each of 32 threads takes the same execution path; the SIMD execution model becomes a significant limitation for any inherently divergent task.
  • No emulation or fallback functionality is available for modern revisions.
  • Valid C++ may sometimes be flagged and prevent compilation due to the way the compiler approaches optimization for target GPU device limitations.
  • C++ run-time type information and C++-style exception handling are only supported in host code, not in device code.
  • In single-precision on first generation CUDA compute capability 1.x devices, denormal numbers are unsupported and are instead flushed to zero, and the precision of both the division and square root operations are slightly lower than IEEE 754-compliant single precision math. Devices that support compute capability 2.0 and above support denormal numbers, and the division and square root operations are IEEE 754 compliant by default. However, users can obtain the prior faster gaming-grade math of compute capability 1.x devices if desired by setting compiler flags to disable accurate divisions and accurate square roots, and enable flushing denormal numbers to zero.
  • Unlike OpenCL, CUDA-enabled GPUs are only available from Nvidia as it is proprietary. Attempts to implement CUDA on other GPUs include:
  • * Project Coriander: Converts CUDA C++11 source to OpenCL 1.2 C. A fork of CUDA-on-CL intended to run TensorFlow.
  • * CU2CL: Convert CUDA 3.2 C++ to OpenCL C.
  • * GPUOpen HIP: A thin abstraction layer on top of CUDA and ROCm intended for AMD and Nvidia GPUs. Has a conversion tool for importing CUDA C++ source. Supports CUDA 4.0 plus C++11 and float16.
  • * ZLUDA is a drop-in replacement for CUDA on AMD GPUs and formerly Intel GPUs with near-native performance. The developer, Andrzej Janik, was separately contracted by both Intel and AMD to develop the software in 2021 and 2022, respectively. However, neither company decided to release it officially due to the lack of a business use case. AMD's contract included a clause that allowed Janik to release his code for AMD independently, allowing him to release the new version that only supports AMD GPUs.
  • * ChipStar can compile and run CUDA/HIP programs on advanced OpenCL 3.0 or Level Zero platforms.
  • * is a CUDA-compatible programming toolkit for ahead of time compilation of CUDA source code on AMD GPUs, aiming to expand support for other GPUs in the future.