CUTLASS 2.2 - June 2020
CUTLASS is a collection of CUDA C++ template abstractions for implementing high-performance matrix-multiplication (GEMM) at all levels and scales within CUDA. It incorporates strategies for hierarchical decomposition and data movement similar to those used to implement cuBLAS. CUTLASS decomposes these "moving parts" into reusable, modular software components abstracted by C++ template classes. These thread-wide, warp-wide, block-wide, and device-wide primitives can be specialized and tuned via custom tiling sizes, data types, and other algorithmic policy. The resulting flexibility simplifies their use as building blocks within custom kernels and applications.
To support a wide variety of applications, CUTLASS provides extensive support for mixed-precision computations, providing specialized data-movement and multiply-accumulate abstractions for half-precision floating point (FP16), BFloat16 (BF16), Tensor Float 32 (TF32), single-precision floating point (FP32), double-precision floating point (FP64) types, integer data types (4b and 8b), and binary data types (1b).
Furthermore, CUTLASS demonstrates warp-synchronous matrix multiply operations targeting the programmable, high-throughput Tensor Cores implemented by NVIDIA's Volta, Turing, and Ampere architectures.
See the Quick Start Guide to get started quickly.
See the functionality listing for the list of operations supported at each level of the execution model hierarchy.
CUTLASS 2.2 is a significant update to CUTLASS adding:
- Coverage of NVIDIA Ampere Architecture features
- Tensor Core-accelerated GEMMs targeting Tensor Float 32, BFloat16, and double-precision data types
- Deep software pipelines using asynchronous copy
- Described in GTC 2020 Webinar (SR 21745)
- Intended to be compiled with CUDA 11 Toolkit
CUTLASS 2.1 is a minor update to CUTLASS 2.0 adding:
- Planar complex GEMM kernels targeting Volta and Turing Tensor Cores
- BLAS-style API to launch kernels compiled into the CUTLASS Library
CUTLASS 2.0 is a substantial refactoring from the previous version, intended to offer:
- Better performance over 1.x, particularly for kernels targeting Turing Tensor Cores
- Robust and durable templates that reliably span the design space
- Encapsulated functionality that may be reusable in other contexts
See the CHANGELOG for more details.
CUTLASS primitives are very efficient. When used to construct device-wide GEMM kernels, they exhibit performance comparable to cuBLAS for scalar GEMM computations. The above figure shows CUTLASS performance relative to cuBLAS for large matrix dimensions on an NVIDIA GeForce 2080 Ti, an NVIDIA A100, and an NVIDIA TitanV using CUDA 11.0 Toolkit. Tensor Core operations are implemented using CUDA's mma instruction.
CUTLASS requires a C++11 host compiler and performs best when built with the CUDA 11.0 Toolkit. It is compatible with CUDA 9.2, CUDA 10.0, CUDA 10.1, and CUDA 10.2.
We have tested the following environments.
| Operating System | Compiler |
|---|---|
| Windows 10 | Microsoft Visual Studio 2015 |
| Microsoft Visual Studio 2017 | |
| Ubuntu 16.04 | GCC 5.4.0 |
| Ubuntu 18.04 | GCC 7.5.0 |
Additionally, CUTLASS may be built with clang. See these instructions for more details.
CUTLASS runs successfully on the following NVIDIA GPUs, and it is expected to be efficient on any Maxwell-, Pascal-, Volta-, Turing-, or NVIDIA Ampere- architecture NVIDIA GPU.
| GPU | CUDA Compute Capability | Minimum CUDA Toolkit | CUDA Toolkit Enabling Native Tensor Cores |
|---|---|---|---|
| NVIDIA Tesla P100 | 6.0 | 9.2 | |
| NVIDIA GeForce 1080 | 6.1 | 9.2 | |
| NVIDIA TitanXP | 6.1 | 9.2 | |
| NVIDIA Tesla V100 | 7.0 | 9.2 | 10.1 |
| NVIDIA TitanV | 7.0 | 9.2 | 10.1 |
| NVIDIA GeForce RTX 2080 TI, 2080, 2070 | 7.5 | 10.0 | 10.2 |
| NVIDIA Tesla T4 | 7.5 | 10.0 | 10.2 |
| NVIDIA A100 | 8.0 | 11.0 | 11.0 |
CUTLASS 2.2 is described in the following documents and the accompanying Doxygen documentation.
- Quick Start Guide - build and run CUTLASS
- Functionality - summarizes functionality available in CUTLASS
- Efficient GEMM in CUDA - describes how GEMM kernels may be implemented efficiently in CUDA
- GEMM API - describes the CUTLASS GEMM model and C++ template concepts
- Code Organization - describes the organization and contents of the CUTLASS project
- Terminology - describes terms used in the code
- Programming Guidelines - guidelines for writing efficient modern CUDA C++
- Fundamental types - describes basic C++ classes used in CUTLASS to represent numeric quantities and arrays
- Layouts - describes layouts of matrices and tensors in memory
- Tile Iterators - describes C++ concepts for iterating over tiles of matrices in memory
- CUTLASS Profiler - command-line driven profiling application
- CUTLASS Utilities - additional templates used to facilate rapid development
We have also described the structure of an efficient GEMM in our talk at the GPU Technology Conference 2018.
CUTLASS is a header-only template library and does not need to be built to be used by other
projects. Client applications should target CUTLASS's include/ directory in their include
paths.
CUTLASS unit tests, examples, and utilities can be build with CMake starting version 3.12.
Make sure the CUDACXX environment variable points to NVCC in the CUDA Toolkit installed
on your system.
$ export CUDACXX=${CUDA_INSTALL_PATH}/bin/nvcc
Create a build directory within the CUTLASS project, then run CMake. By default CUTLASS will build kernels
for CUDA architecture versions 5.0, 6.0, 6.1, 7.0, 7.5, and 8.0. To reduce compile time you can specify
the architectures to build CUTLASS for by changing the CMake configuration setting
CUTLASS_NVCC_ARCHS.
$ mkdir build && cd build
$ cmake .. -DCUTLASS_NVCC_ARCHS=75 # compiles for NVIDIA's Turing GPU architecture
From the build/ directory, compile and run the CUTLASS unit tests by building the target test_unit with make.
The unit tests are organized as several binaries mirroring the top-level namespaces of CUTLASS,
and they may be executed in parallel via make's -j command line argument.
$ make test_unit -j
...
...
...
[----------] Global test environment tear-down
[==========] 946 tests from 57 test cases ran. (10812 ms total)
[ PASSED ] 946 tests.
All tests should pass on supported platforms, though the exact number of tests may vary over time.
CUTLASS is arranged as a header-only library along with Utilities, Tools, Examples, and unit tests. Doxygen documentation provides a complete list of files, classes, and template concepts defined in the CUTLASS project.
A detailed explanation of the source code organization may be found in the CUTLASS documentation, but several main components are summarized below.
include/ # client applications should target this directory in their build's include paths
cutlass/ # CUDA Templates for Linear Algebra Subroutines and Solvers - headers only
arch/ # direct exposure of architecture features (including instruction-level GEMMs)
gemm/ # code specialized for general matrix product computations
layout/ # layout definitions for matrices, tensors, and other mathematical objects in memory
platform/ # CUDA-capable Standard Library components
reduction/ # bandwidth-limited reduction kernels that do not fit the "gemm" model
transform/ # code specialized for layout, type, and domain transformations
* # core vocabulary types, containers, and basic numeric operations
CUTLASS SDK examples apply CUTLASS templates to implement basic computations.
examples/
00_basic_gemm/ # launches a basic GEMM with single precision inputs and outputs
01_cutlass_utilities/ # demonstrates CUTLASS Utilities for allocating and initializing tensors
02_dump_reg_smem/ # debugging utilities for printing register and shared memory contents
03_visualize_layout/ # utility for visualizing all layout functions in CUTLASS
04_tile_iterator/ # example demonstrating an iterator over tiles in memory
05_batched_gemm/ # example demonstrating CUTLASS's batched strided GEMM operation
06_splitK_gemm/ # exmaple demonstrating CUTLASS's Split-K parallel reduction kernel
07_volta_tensorop_gemm/ # example demonstrating mixed precision GEMM using Volta Tensor Cores
08_turing_tensorop_gemm/ # example demonstrating integer GEMM using Turing Tensor Cores
10_planar_complex/ # example demonstrating planar complex GEMM kernels
11_planar_complex_array/ # example demonstrating planar complex kernels with batch-specific problem sizes
12_gemm_bias_relu/ # example demonstrating GEMM fused with bias and relu
13_fused_two_gemms/ # example demonstrating two GEMms fused in one kernel
tools/
library/ # CUTLASS Instance Library - contains instantiations of all supported CUTLASS templates
include/
cutlass/
library/
profiler/ # CUTLASS Profiler - command-line utility for executing operations in the
# CUTLASS Library
util/ # CUTLASS Utilities - contains numerous helper classes for
include/ # manging tensors in device memory, reference
cutlass/ # implementations for GEMM, random initialization
util/ # of tensors, and I/O.
The test/unit/ directory consist of unit tests implemented with Google Test that demonstrate
basic usage of Core API components and complete tests of the CUTLASS GEMM computations.
Instructions for building and running the Unit tests are described in the Quickstart guide.
The tools/profiler/ directory contains a command-line utility for launching each of the GEMM kernels.
It can be built as follows:
$ make cutlass_profiler -j
To limit compilation time, only one tile size is instantiated for each data type, math instruction, and layout.
To instantiate all, set the following environment variable when running CMake from an empty build/ directory.
$ cmake .. -DCUTLASS_NVCC_ARCHS=75 -DCUTLASS_LIBRARY_KERNELS=all
...
$ make cutlass_profiler -j
Example command line for profiling SGEMM kernels is as follows:
$ ./tools/profiler/cutlass_profiler --kernels=sgemm --m=3456 --n=4096 --k=4096
=============================
Problem ID: 1
Provider: CUTLASS
OperationKind: gemm
Operation: cutlass_simt_sgemm_128x128_8x2_nn_align1
Status: Success
Verification: ON
Disposition: Passed
cuBLAS: Passed
Arguments: --m=3456 --n=4096 --k=4096 --A=f32:column --B=f32:column --C=f32:column --alpha=1 --beta=0 --split_k_slices=1 \
--batch_count=1 --op_class=simt --accum=f32 --cta_m=128 --cta_n=128 --cta_k=8 --stages=2 --warps_m=4 \
--warps_n=2 --warps_k=1 --inst_m=1 --inst_n=1 --inst_k=1 --min_cc=50 --max_cc=1024
Bytes: 180355072 bytes
FLOPs: 115992428544 flops
Runtime: 6.73655 ms
Memory: 24.934 GiB/s
Math: 17218.4 GFLOP/s
Further details about the CUTLASS Profiler are described here.
CUTLASS is released by NVIDIA Corporation as Open Source software under the 3-clause "New" BSD license.
The official list of CUTLASS developers and contributors is available here: CONTRIBUTORS.
Copyright (c) 2017-2020, NVIDIA CORPORATION. All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted
provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice, this list of
conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice, this list of
conditions and the following disclaimer in the documentation and/or other materials
provided with the distribution.
* Neither the name of the NVIDIA CORPORATION nor the names of its contributors may be used
to endorse or promote products derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NVIDIA CORPORATION BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TOR (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.