CUTLASS 2.9 - April 2022
CUTLASS is a collection of CUDA C++ template abstractions for implementing high-performance matrix-multiplication (GEMM) and related computations at all levels and scales within CUDA. It incorporates strategies for hierarchical decomposition and data movement similar to those used to implement cuBLAS and cuDNN. 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). CUTLASS demonstrates warp-synchronous matrix multiply operations targeting the programmable, high-throughput Tensor Cores implemented by NVIDIA's Volta, Turing, and Ampere architectures.
CUTLASS implements high-performance Convolution via the implicit GEMM algorithm. Implicit GEMM is the formulation of a convolution operation as a GEMM thereby taking advantage of CUTLASS's modular GEMM pipeline. This allows CUTLASS to build convolutions by reusing highly optimized warp-wide GEMM components and below.
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 2.9 is an update to CUTLASS adding:
- First layer Convolution kernels specialized for small channel counts and reduced alignment
- BLAS3 operators accelerated by Tensor Cores
- CUTLASS Python demonstrating JIT compilation of CUTLASS kernels and a Python-based runtime using CUDA Python
- GEMM + Softmax example
- Gather and Scatter Fusion with GEMM can gather inputs and scatters outputs based on indices vectors in the same GEMM kernel.
- Back-to-back GEMM/CONV fully supports buffering the first GEMM/CONV results in the shared memory for the latter one to use. Bias Vector add is also supported in the first GEMM/CONV.
- Transposed Convolution (a.k.a Deconvolution) support which reuses Dgrad implementation.
- Utility functions that can pad NHWC and convert between NCHW and NHWC.
- Small alignment implicit gemm support for Fprop/Dgrad/Wgrad so that padding is no longer mandated to use tensor cores.
- Epilogue enhancement with performance improvement, more activation functions, and more fusion patterns.
- Group GEMM thread block number calculation fix.
- Optimal performance using CUDA 11.7
- Parallel GEMM splitk support in the CUTLASS profiler.
- Updates and bugfixes from the community (thanks!)
- Deprecation announcement: CUTLASS plans to deprecate the following:
- Maxwell and Pascal GPU architectures
- Ubuntu 16.04
- CUDA 10.2
See the CHANGELOG for a detailed listing of releases and updates.
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 A100, an NVIDIA A2, an NVIDIA TitanV, and an NVIDIA GeForce 2080 Ti compiled with the CUDA 11.5 Toolkit. Tensor Core operations are implemented using CUDA's mma instruction.
When using CUTLASS building blocks to construct device-wide implicit gemm (Fprop, Dgrad, and Wgrad) kernels, CUTLASS performance is also comparable to cuDNN when running Resnet-50 layers on an NVIDIA A100 as shown in the above figure. Tensor Core operations are still implemented using CUDA's mma instruction.
CUTLASS requires a C++11 host compiler and performs best when built with the CUDA 11.6u2 Toolkit. It is also compatible with CUDA 11.0, CUDA 11.1, CUDA 11.2, CUDA 11.3, CUDA 11.4, and CUDA 11.5.
We have tested the following environments.
| Operating System | Compiler |
|---|---|
| Windows 10 | Microsoft Visual Studio 2015 |
| Microsoft Visual Studio 2017 | |
| Microsoft Visual Studio 2019 | |
| Ubuntu 18.04 | GCC 7.5.0 |
| Ubuntu 20.04 | GCC 10.3.0 |
| Ubuntu 21.04 | GCC 11.2.0 |
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 Volta-, Turing-, or NVIDIA Ampere- architecture NVIDIA GPU.
| GPU | CUDA Compute Capability | Minimum CUDA Toolkit | Minimum CUDA Toolkit Enabling Native Tensor Cores |
|---|---|---|---|
| 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 |
| NVIDIA A10 | 8.6 | 11.1 | 11.1 |
| NVIDIA GeForce 3090 | 8.6 | 11.1 | 11.1 |
For all GPUs, we recommend compiling with the CUDA 11.6u2 Toolkit for best performance.
CUTLASS 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
- Implicit GEMM Convolution - describes 2-D and 3-D convolution in CUTLASS
- 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/nvccCreate 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, 8.0, and 8.6. 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=80 # compiles for NVIDIA's Ampere ArchitectureFrom 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)
conv/ # code specialized for convolution
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
09_turing_tensorop_conv2dfprop/ # example demonstrating integer implicit GEMM convolution (forward propagation) 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
22_ampere_tensorop_conv2dfprop/ # example demonstrating integer implicit GEMM convolution (forward propagation) using Ampere Tensor Cores
31_basic_syrk # example demonstrating Symetric rank-K update
32_basic_trmm #
33_ampere_3xtf32_tensorop_symm #
35_gemm_softmax # example demonstrating GEMM fused with Softmax in mixed precision using Ampere Tensor Cores
40_cutlass_py # example demonstrating CUTLASS with CUDA Python
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 -j16By default, 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.
Beware, this results in thousands of kernels and long build times.
$ cmake .. -DCUTLASS_NVCC_ARCHS=75 -DCUTLASS_LIBRARY_KERNELS=all
...
$ make cutlass_profiler -j16To compile strictly one kernel or a small set of kernels, a comma-delimited list of kernel names with wildcard characters may be used to reduce the set of kernels. The following examples show building exactly one or a subset of kernels for NVIDIA Ampere and Turing architecture:
To compile a subset of Tensor Core GEMM kernels with FP32 accumulation and FP16 input targetting NVIDIA Ampere and Turing architecture, use the below cmake command line:
$ cmake .. -DCUTLASS_NVCC_ARCHS='75;80' -DCUTLASS_LIBRARY_KERNELS=cutlass_tensorop_s*gemm_f16_*_nt_align8
...
$ make cutlass_profiler -j16Example command line for profiling a subset of Tensor Core GEMM kernels is as follows:
./tools/profiler/cutlass_profiler --kernels=cutlass_tensorop_s*gemm_f16_*_nt_align8 --m=3456 --n=4096 --k=4096
...
=============================
Problem ID: 1
Provider: CUTLASS
OperationKind: gemm
Operation: cutlass_tensorop_s1688gemm_f16_256x128_32x2_nt_align8
Status: Success
Verification: ON
Disposition: Passed
reference_device: Passed
cuBLAS: Passed
Arguments: --gemm_kind=universal --m=3456 --n=4096 --k=4096 --A=f16:column --B=f16:row --C=f32:column --alpha=1 \
--beta=0 --split_k_slices=1 --batch_count=1 --op_class=tensorop --accum=f32 --cta_m=256 --cta_n=128 \
--cta_k=32 --stages=2 --warps_m=4 --warps_n=2 --warps_k=1 --inst_m=16 --inst_n=8 --inst_k=8 --min_cc=75 \
--max_cc=1024
Bytes: 118489088 bytes
FLOPs: 115992428544 flops
Runtime: 1.55948 ms
Memory: 70.7616 GiB/s
Math: 74378.8 GFLOP/s
=============================
...To compile one SGEMM kernel targetting NVIDIA Ampere and Turing architecture, use the below cmake command line:
$ cmake .. -DCUTLASS_NVCC_ARCHS='75;80' -DCUTLASS_LIBRARY_KERNELS=cutlass_simt_sgemm_128x128_8x2_nn_align1
...
$ make cutlass_profiler -j16Example command line for profiling single SGEMM CUDA kernel 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
=============================To compile a subset of Tensor core convolution kernels implementing forward propagation (fprop) with FP32 accumulation and FP16 input targetting NVIDIA Ampere and Turing architecture, use the below cmake command line:
$ cmake .. -DCUTLASS_NVCC_ARCHS='75;80' -DCUTLASS_LIBRARY_KERNELS=cutlass_tensorop_s*fprop_optimized_f16
...
$ make cutlass_profiler -j16Example command line for profiling a subset of Tensor Core convolution kernels is as follows:
$ ./tools/profiler/cutlass_profiler --kernels=cutlass_tensorop_s*fprop_optimized_f16 --n=8 --h=224 --w=224 --c=128 --k=128 --r=3 --s=3
...
=============================
Problem ID: 1
Provider: CUTLASS
OperationKind: conv2d
Operation: cutlass_tensorop_s16816fprop_optimized_f16_128x128_32x5_nhwc
Status: Success
Verification: ON
Disposition: Passed
reference_device: Passed
Arguments: --conv_kind=fprop --n=8 --h=224 --w=224 --c=128 --k=128 --r=3 --s=3 --p=224 --q=224 --pad_h=1 --pad_w=1 \
--stride_h=1 --stride_w=1 --dilation_h=1 --dilation_w=1 --Activation=f16:nhwc --Filter=f16:nhwc --Output=f32:nhwc \
--conv_mode=cross --iterator_algorithm=optimized --alpha=1 --beta=0 --split_k_mode=serial --split_k_slices=1 \
--eq_gemm_provider=none --op_class=tensorop --accum=f32 --cta_m=128 --cta_n=128 --cta_k=32 --stages=5 \
--warps_m=2 --warps_n=2 --warps_k=1 --inst_m=16 --inst_n=8 --inst_k=16 --min_cc=80 --max_cc=1024
Bytes: 1130659840 bytes
FLOPs: 118482796544 flops
Runtime: 0.711496 ms
Memory: 1479.99 GiB/s
Math: 166526 GFLOP/s
=============================
...To compile and run one CUDA Core convolution kernel implementing forward propagation (fprop) with F32 accumulation and FP32 input targetting NVIDIA Ampere and Turing architecture, use the below cmake command line:
$ cmake .. -DCUTLASS_NVCC_ARCHS='75;80' -DCUTLASS_LIBRARY_KERNELS=cutlass_simt_sfprop_optimized_128x128_8x2_nhwc
...
$ make cutlass_profiler -j16Example command line for profiling one CUDA Core convolution kernel:
$ ./tools/profiler/cutlass_profiler --kernels=cutlass_simt_sfprop_optimized_128x128_8x2_nhwc --n=8 --h=224 --w=224 --c=128 --k=128 --r=3 --s=3
=============================
Problem ID: 1
Provider: CUTLASS
OperationKind: conv2d
Operation: cutlass_simt_sfprop_optimized_128x128_8x2_nhwc
Status: Success
Verification: ON
Disposition: Passed
reference_device: Passed
Arguments: --conv_kind=fprop --n=8 --h=224 --w=224 --c=128 --k=128 --r=3 --s=3 --p=224 --q=224 --pad_h=1 --pad_w=1 \
--stride_h=1 --stride_w=1 --dilation_h=1 --dilation_w=1 --Activation=f32:nhwc --Filter=f32:nhwc --Output=f32:nhwc \
--conv_mode=cross --iterator_algorithm=optimized --alpha=1 --beta=0 --split_k_mode=serial --split_k_slices=1 \
--eq_gemm_provider=none --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: 2055798784 bytes
FLOPs: 118482796544 flops
Runtime: 7.34266 ms
Memory: 260.752 GiB/s
Math: 16136.2 GFLOP/s
=============================
- Please follow the links for more CMake examples on selectively compiling CUTLASS kernels:
- 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 - 2022 NVIDIA CORPORATION & AFFILIATES. All rights reserved. SPDX-License-Identifier: BSD-3-Clause
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