- Contributing to PyTorch
- Developing PyTorch
- Nightly Checkout & Pull
- Codebase structure
- Unit testing
- Merging your Change
- Writing documentation
- Profiling with
py-spy
- Managing multiple build trees
- C++ development tips
- CUDA development tips
- Windows development tips
- Running clang-tidy
- Pre-commit tidy/linting hook
- Building PyTorch with ASAN
- Caffe2 notes
- CI failure tips
- Dev Infra Office Hours
Thank you for your interest in contributing to PyTorch! Before you begin writing code, it is important that you share your intention to contribute with the team, based on the type of contribution:
- You want to propose a new feature and implement it.
- Post about your intended feature in an issue, and we shall discuss the design and implementation. Once we agree that the plan looks good, go ahead and implement it.
- You want to implement a feature or bug-fix for an outstanding issue.
- Search for your issue in the PyTorch issue list.
- Pick an issue and comment that you'd like to work on the feature or bug-fix.
- If you need more context on a particular issue, please ask and we shall provide.
Once you implement and test your feature or bug-fix, please submit a Pull Request to https://github.com/pytorch/pytorch.
This document covers some of the more technical aspects of contributing to PyTorch. For more non-technical guidance about how to contribute to PyTorch, see the Contributing Guide.
Follow the instructions for installing PyTorch from source. If you get stuck when developing PyTorch on your machine, check out the tips and debugging section below for common solutions.
-
If you want to have no-op incremental rebuilds (which are fast), see Make no-op build fast below.
-
When installing with
python setup.py develop
(in contrast topython setup.py install
) you will symlink the Python files from the current local source-tree into the Python install. This way you do not need to repeatedly install after modifying Python files (.py
). However, you would need to reinstall if you modify Python interface (.pyi
,.pyi.in
) or non-Python files (.cpp
,.cc
,.cu
,.h
, ...).To reinstall, first uninstall all existing PyTorch installs. You may need to run
pip uninstall torch
multiple times. You'll knowtorch
is fully uninstalled when you seeWARNING: Skipping torch as it is not installed
. (You should only have topip uninstall
a few times, but you can alwaysuninstall
withtimeout
or in a loop if you're feeling lazy.)conda uninstall pytorch -y yes | pip uninstall torch
Next run
python setup.py clean
. After that, you can install indevelop
mode again. -
If a commit is simple and doesn't affect any code (keep in mind that some docstrings contain code that is used in tests), you can add
[skip ci]
(case sensitive) somewhere in your commit message to skip all build / test steps. Note that changing the pull request body or title on GitHub itself has no effect. -
If you run into errors when running
python setup.py develop
, here are some debugging steps:- Run
printf '#include <stdio.h>\nint main() { printf("Hello World");}'|clang -x c -; ./a.out
to make sure your CMake works and can compile this simple Hello World program without errors. - Nuke your
build
directory. Thesetup.py
script compiles binaries into thebuild
folder and caches many details along the way, which saves time the next time you build. If you're running into issues, you can alwaysrm -rf build
from the toplevelpytorch
directory and start over. - If you have made edits to the PyTorch repo, commit any change you'd like to keep and clean the repo with the
following commands (note that clean really removes all untracked files and changes.):
git submodule deinit -f . git clean -xdf python setup.py clean git submodule update --init --recursive # very important to sync the submodules python setup.py develop # then try running the command again
- The main step within
python setup.py develop
is runningmake
from thebuild
directory. If you want to experiment with some environment variables, you can pass them into the command:ENV_KEY1=ENV_VAL1[, ENV_KEY2=ENV_VAL2]* python setup.py develop
- Run
-
If you run into issue running
git submodule update --init --recursive
. Please try the following:-
If you encounter an error such as
error: Submodule 'third_party/pybind11' could not be updated
check whether your Git local or global config file contains any
submodule.*
settings. If yes, remove them and try again. (please reference this doc for more info). -
If you encounter an error such as
fatal: unable to access 'https://github.com/pybind11/pybind11.git': could not load PEM client certificate ...
this is likely that you are using HTTP proxying and the certificate expired. To check if the certificate is valid, run
git config --global --list
and search for config likehttp.proxysslcert=<cert_file>
. Then check certificate valid date by runningopenssl x509 -noout -in <cert_file> -dates
-
If you encounter an error that some third_party modules are not checked out correctly, such as
Could not find .../pytorch/third_party/pybind11/CMakeLists.txt
remove any
submodule.*
settings in your local git config (.git/config
of your pytorch repo) and try again.
-
-
If you're a Windows contributor, please check out Best Practices.
-
For help with any part of the contributing process, please don’t hesitate to utilize our Zoom office hours! See details here
The tools/nightly.py
script is provided to ease pure Python development of
PyTorch. This uses conda
and git
to check out the nightly development
version of PyTorch and installs pre-built binaries into the current repository.
This is like a development or editable install, but without needing the ability
to compile any C++ code.
You can use this script to check out a new nightly branch with the following:
./tools/nightly.py checkout -b my-nightly-branch
conda activate pytorch-deps
Or if you would like to re-use an existing conda environment, you can pass in
the regular environment parameters (--name
or --prefix
):
./tools/nightly.py checkout -b my-nightly-branch -n my-env
conda activate my-env
You can also use this tool to pull the nightly commits into the current branch:
./tools/nightly.py pull -n my-env
conda activate my-env
Pulling will reinstall the PyTorch dependencies as well as the nightly binaries into the repo directory.
- c10 - Core library files that work everywhere, both server and mobile. We are slowly moving pieces from ATen/core here. This library is intended only to contain essential functionality, and appropriate to use in settings where binary size matters. (But you'll have a lot of missing functionality if you try to use it directly.)
- aten - C++ tensor library for PyTorch (no autograd support)
- src - README
- ATen
- core - Core functionality of ATen. This is migrating to top-level c10 folder.
- native - Modern implementations of
operators. If you want to write a new operator, here is where
it should go. Most CPU operators go in the top level directory,
except for operators which need to be compiled specially; see
cpu below.
- cpu - Not actually CPU implementations of operators, but specifically implementations which are compiled with processor-specific instructions, like AVX. See the README for more details.
- cuda - CUDA implementations of operators.
- sparse - CPU and CUDA implementations of COO sparse tensor operations
- mkl mkldnn
miopen cudnn
- implementations of operators which simply bind to some backend library.
- quantized - Quantized tensor (i.e. QTensor) operation implementations. README contains details including how to implement native quantized operations.
- ATen
- src - README
- torch - The actual PyTorch library. Everything that is not in csrc is a Python module, following the PyTorch Python frontend module structure.
- tools - Code generation scripts for the PyTorch library. See README of this directory for more details.
- test - Python unit tests for PyTorch Python frontend.
- test_torch.py - Basic tests for PyTorch functionality.
- test_autograd.py - Tests for non-NN automatic differentiation support.
- test_nn.py - Tests for NN operators and their automatic differentiation.
- test_jit.py - Tests for the JIT compiler and TorchScript.
- ...
- cpp - C++ unit tests for PyTorch C++ frontend.
- expect - Automatically generated "expect" files which are used to compare against expected output.
- onnx - Tests for ONNX export functionality, using both PyTorch and Caffe2.
- caffe2 - The Caffe2 library.
- .circleci - CircleCI configuration management. README
Prerequisites:
The following packages should be installed with either conda
or pip
:
expecttest
andhypothesis
- required to run testsmypy
- recommended for lintingpytest
- recommended to run tests more selectively
All PyTorch test suites are located in the test
folder and start with
test_
. Run the entire test
suite with
python test/run_test.py
or run individual test suites using the command python test/FILENAME.py
,
where FILENAME
represents the file containing the test suite you wish
to run.
For example, to run all the TorchScript JIT tests (located at
test/test_jit.py
), you would run:
python test/test_jit.py
You can narrow down what you're testing even further by specifying the
name of an individual test with TESTCLASSNAME.TESTNAME
. Here,
TESTNAME
is the name of the test you want to run, and TESTCLASSNAME
is the name of the class in which it is defined.
Going off the above example, let's say you want to run
test_Sequential
, which is defined as part of the TestJit
class
in test/test_jit.py
. Your command would be:
python test/test_jit.py TestJit.test_Sequential
Weird note: In our CI (Continuous Integration) jobs, we actually run the tests from the test
folder and not the root of the repo, since there are various dependencies we set up for CI that expects the tests to be run from the test folder. As such, there may be some inconsistencies between local testing and CI testing--if you observe an inconsistency, please file an issue.
We don't officially support pytest
, but it works well with our
unittest
tests and offers a number of useful features for local
developing. Install it via pip install pytest
.
If you want to just run tests that contain a specific substring, you can
use the -k
flag:
pytest test/test_nn.py -k Loss -v
The above is an example of testing a change to all Loss functions: this
command runs tests such as TestNN.test_BCELoss
and
TestNN.test_MSELoss
and can be useful to save keystrokes.
Install all prerequisites by running
make setup_lint
You can now run the same linting steps that are used in CI locally via make
:
make lint
Learn more about the linter on the lintrunner wiki page
mypy
is an optional static type checker for Python. We have multiple mypy
configs for the PyTorch codebase that are automatically validated against whenever the linter is run.
See Guide for adding type annotations to
PyTorch
for more information on how to set up mypy
and tackle type annotation
tasks.
PyTorch offers a series of tests located in the test/cpp
folder.
These tests are written in C++ and use the Google Test testing framework.
After compiling PyTorch from source, the test runner binaries will be
written to the build/bin
folder. The command to run one of these tests
is ./build/bin/FILENAME --gtest_filter=TESTSUITE.TESTNAME
, where
TESTNAME
is the name of the test you'd like to run and TESTSUITE
is
the suite that test is defined in.
For example, if you wanted to run the test MayContainAlias
, which
is part of the test suite ContainerAliasingTest
in the file
test/cpp/jit/test_alias_analysis.cpp
, the command would be:
./build/bin/test_jit --gtest_filter=ContainerAliasingTest.MayContainAlias
You can generate a commit that limits the CI to only run a specific job by using
tools/testing/explicit_ci_jobs.py
like so:
# --job: specify one or more times to filter to a specific job + its dependencies
# --filter-gha: specify github actions workflows to keep
# --make-commit: commit CI changes to git with a message explaining the change
python tools/testing/explicit_ci_jobs.py --job binary_linux_manywheel_3_6m_cpu_devtoolset7_nightly_test --filter-gha '*generated*gcc5.4*' --make-commit
# Make your changes
ghstack submit
NB: It is not recommended to use this workflow unless you are also using
ghstack
. It creates a large commit that is
of very low signal to reviewers.
If you know the right people or team that should approve your PR (and you have the required permissions to do so), add them to the Reviewers list.
If not, leave the Reviewers section empty. Our triage squad will review your PR, add a module label, and assign it to the appropriate reviewer in a couple business days. The reviewer will then look at your PR and respond.
Occasionally, things might fall through the cracks (sorry!). In case your PR either doesn't get assigned to a reviewer or doesn't get any response from the reviewer for 4 business days, please leave comment on the PR (mentioning the reviewer if one has been assigned). That'll get it nudged back onto people's radar.
If that still doesn't help, come see us during our office hours
Once your PR is approved, you can merge it in by entering a comment with the content @pytorchmergebot merge
(what's this bot?)
So you want to write some documentation and don't know where to start? PyTorch has two main types of documentation:
- User facing documentation: These are the docs that you see over at our docs website.
- Developer facing documentation: Developer facing documentation is spread around our READMEs in our codebase and in the PyTorch Developer Wiki. If you're interested in adding new developer docs, please read this page on the wiki on our best practices for where to put it.
The rest of this section is about user-facing documentation.
PyTorch uses Google style for formatting docstrings. Each line inside a docstrings block must be limited to 80 characters so that it fits into Jupyter documentation popups.
In addition to the standard Google Style docstring formatting rules, the following guidelines should be followed for docstring types (docstring types are the type information contained in the round brackets after the variable name):
-
The "
Callable
", "Any
", "Iterable
", "Iterator
", "Generator
" types should have their first letter capitalized. -
The "
list
" and "tuple
" types should be completely lowercase. -
Types should not be made plural. For example:
tuple of int
should be used instead oftuple of ints
. -
The only acceptable delimiter words for types are
or
andof
. No other non-type words should be used other thanoptional
. -
The word
optional
should only be used after the types, and it is only used if the user does not have to specify a value for the variable. Default values are listed after the variable description. Example:my_var (int, optional): Variable description. Default: 1
-
Basic Python types should match their type name so that the Intersphinx extension can correctly identify them. For example:
- Use
str
instead ofstring
. - Use
bool
instead ofboolean
. - Use
dict
instead ofdictionary
.
- Use
-
Square brackets should be used for the dictionary type. For example:
my_var (dict[str, int]): Variable description.
-
If a variable has two different possible types, then the word
or
should be used without a comma. Otherwise variables with 3 or more types should use commas to separate the types. Example:x (type1 or type2): Variable description. y (type1, type2, or type3): Variable description.
To build the documentation:
-
Build and install PyTorch
-
Install the prerequisites
cd docs
pip install -r requirements.txt
# `katex` must also be available in your PATH.
# You can either install katex globally if you have properly configured npm:
# npm install -g katex
# Or if you prefer an uncontaminated global executable environment or do not want to go through the node configuration:
# npm install katex && export PATH="$PATH:$(pwd)/node_modules/.bin"
Note: if you installed
nodejs
with a different package manager (e.g.,conda
) thennpm
will probably install a version ofkatex
that is not compatible with your version ofnodejs
and doc builds will fail. A combination of versions that is known to work is[email protected]
and[email protected]
. To install the latter withnpm
you can runnpm install -g [email protected]
Note that if you are a Facebook employee using a devserver, yarn may be more convenient to install katex:
yarn global add katex
If a specific version is required you can use for example
yarn global add [email protected]
.
- Generate the documentation HTML files. The generated files will be in
docs/build/html
.
make html
The .rst
source files live in docs/source. Some of the .rst
files pull in docstrings from PyTorch Python code (for example, via
the autofunction
or autoclass
directives). To vastly shorten doc build times,
it is helpful to remove the files you are not working on, only keeping the base
index.rst
file and the files you are editing. The Sphinx build will produce
missing file warnings but will still complete. For example, to work on jit.rst
:
cd docs/source
find . -type f | grep rst | grep -v index | grep -v jit | xargs rm
# Make your changes, build the docs, etc.
# Don't commit the deletions!
git add index.rst jit.rst
...
For C++ documentation (https://pytorch.org/cppdocs), we use Doxygen and then convert it to Sphinx via Breathe and Exhale. Check the Doxygen reference for more information on the documentation syntax.
We run Doxygen in CI (Travis) to verify that you do not use invalid Doxygen
commands. To run this check locally, run ./check-doxygen.sh
from inside
docs/cpp/source
.
To build the documentation, follow the same steps as above, but run them from
docs/cpp
instead of docs
.
To view HTML files locally, you can open the files in your web browser. For example,
navigate to file:///your_pytorch_folder/docs/build/html/index.html
in a web
browser.
If you are developing on a remote machine, you can set up an SSH tunnel so that you can access the HTTP server on the remote machine from your local machine. To map remote port 8000 to local port 8000, use either of the following commands.
# For SSH
ssh my_machine -L 8000:my_machine:8000
# For Eternal Terminal
et my_machine -t="8000:8000"
Then navigate to localhost:8000
in your web browser.
Tip: You can start a lightweight HTTP server on the remote machine with:
python -m http.server 8000 <path_to_html_output>
Alternatively, you can run rsync
on your local machine to copy the files from
your remote machine:
mkdir -p build cpp/build
rsync -az me@my_machine:/path/to/pytorch/docs/build/html build
rsync -az me@my_machine:/path/to/pytorch/docs/cpp/build/html cpp/build
PyTorch will host documentation previews at https://docs-preview.pytorch.org/<pr number>/
once the
pytorch_python_doc_build
GitHub Actions job has completed on your PR. You can visit that page directly
or find its link in the automated Dr. CI comment on your PR.
It is easy for code snippets in docstrings and .rst
files to get out of date. The docs
build includes the Sphinx Doctest Extension,
which can run code in documentation as a unit test. To use the extension, use
the .. testcode::
directive in your .rst
and docstrings.
To manually run these tests, follow steps 1 and 2 above, then run:
cd docs
make doctest
Evaluating the performance impact of code changes in PyTorch can be complicated,
particularly if code changes happen in compiled code. One simple way to profile
both Python and C++ code in PyTorch is to use
py-spy
, a sampling profiler for Python
that has the ability to profile native code and Python code in the same session.
py-spy
can be installed via pip
:
pip install py-spy
To use py-spy
, first write a Python test script that exercises the
functionality you would like to profile. For example, this script profiles
torch.add
:
import torch
t1 = torch.tensor([[1, 1], [1, 1.]])
t2 = torch.tensor([[0, 0], [0, 0.]])
for _ in range(1000000):
torch.add(t1, t2)
Since the torch.add
operation happens in microseconds, we repeat it a large
number of times to get good statistics. The most straightforward way to use
py-spy
with such a script is to generate a flame
graph:
py-spy record -o profile.svg --native -- python test_tensor_tensor_add.py
This will output a file named profile.svg
containing a flame graph you can
view in a web browser or SVG viewer. Individual stack frame entries in the graph
can be selected interactively with your mouse to zoom in on a particular part of
the program execution timeline. The --native
command-line option tells
py-spy
to record stack frame entries for PyTorch C++ code. To get line numbers
for C++ code it may be necessary to compile PyTorch in debug mode by prepending
your setup.py develop
call to compile PyTorch with DEBUG=1
. Depending on
your operating system it may also be necessary to run py-spy
with root
privileges.
py-spy
can also work in an htop
-like "live profiling" mode and can be
tweaked to adjust the stack sampling rate, see the py-spy
readme for more
details.
One downside to using python setup.py develop
is that your development
version of PyTorch will be installed globally on your account (e.g., if
you run import torch
anywhere else, the development version will be
used.
If you want to manage multiple builds of PyTorch, you can make use of conda environments to maintain separate Python package environments, each of which can be tied to a specific build of PyTorch. To set one up:
conda create -n pytorch-myfeature
source activate pytorch-myfeature
# if you run python now, torch will NOT be installed
python setup.py develop
If you are working on the C++ code, there are a few important things that you will want to keep in mind:
- How to rebuild only the code you are working on.
- How to make rebuilds in the absence of changes go faster.
python setup.py build
will build everything by default, but sometimes you are
only interested in a specific component.
- Working on a test binary? Run
(cd build && ninja bin/test_binary_name)
to rebuild only that test binary (without rerunning cmake). (Replaceninja
withmake
if you don't have ninja installed). - Don't need Caffe2? Pass
BUILD_CAFFE2=0
to disable Caffe2 build.
On the initial build, you can also speed things up with the environment
variables DEBUG
, USE_DISTRIBUTED
, USE_MKLDNN
, USE_CUDA
, BUILD_TEST
, USE_FBGEMM
, USE_NNPACK
and USE_QNNPACK
.
DEBUG=1
will enable debug builds (-g -O0)REL_WITH_DEB_INFO=1
will enable debug symbols with optimizations (-g -O3)USE_DISTRIBUTED=0
will disable distributed (c10d, gloo, mpi, etc.) build.USE_MKLDNN=0
will disable using MKL-DNN.USE_CUDA=0
will disable compiling CUDA (in case you are developing on something not CUDA related), to save compile time.BUILD_TEST=0
will disable building C++ test binaries.USE_FBGEMM=0
will disable using FBGEMM (quantized 8-bit server operators).USE_NNPACK=0
will disable compiling with NNPACK.USE_QNNPACK=0
will disable QNNPACK build (quantized 8-bit operators).USE_XNNPACK=0
will disable compiling with XNNPACK.
For example:
DEBUG=1 USE_DISTRIBUTED=0 USE_MKLDNN=0 USE_CUDA=0 BUILD_TEST=0 USE_FBGEMM=0 USE_NNPACK=0 USE_QNNPACK=0 USE_XNNPACK=0 python setup.py develop
For subsequent builds (i.e., when build/CMakeCache.txt
exists), the build
options passed for the first time will persist; please run ccmake build/
, run
cmake-gui build/
, or directly edit build/CMakeCache.txt
to adapt build
options.
When using python setup.py develop
, PyTorch will generate
a compile_commands.json
file that can be used by many editors
to provide command completion and error highlighting for PyTorch's
C++ code. You need to pip install ninja
to generate accurate
information for the code in torch/csrc
. More information at:
By default, cmake will use its Makefile generator to generate your build
system. You can get faster builds if you install the ninja build system
with pip install ninja
. If PyTorch was already built, you will need
to run python setup.py clean
once after installing ninja for builds to
succeed.
Even when dependencies are tracked with file modification, there are many situations where files get rebuilt when a previous compilation was exactly the same. Using ccache in a situation like this is a real time-saver.
Before building pytorch, install ccache from your package manager of choice:
conda install ccache -c conda-forge
sudo apt install ccache
sudo yum install ccache
brew install ccache
You may also find the default cache size in ccache is too small to be useful. The cache sizes can be increased from the command line:
# config: cache dir is ~/.ccache, conf file ~/.ccache/ccache.conf
# max size of cache
ccache -M 25Gi # -M 0 for unlimited
# unlimited number of files
ccache -F 0
To check this is working, do two clean builds of pytorch in a row. The second
build should be substantially and noticeably faster than the first build. If
this doesn't seem to be the case, check the CMAKE_<LANG>_COMPILER_LAUNCHER
rules in build/CMakeCache.txt
, where <LANG>
is C
, CXX
and CUDA
.
Each of these 3 variables should contain ccache, e.g.
//CXX compiler launcher
CMAKE_CXX_COMPILER_LAUNCHER:STRING=/usr/bin/ccache
If not, you can define these variables on the command line before invoking setup.py
.
export CMAKE_C_COMPILER_LAUNCHER=ccache
export CMAKE_CXX_COMPILER_LAUNCHER=ccache
export CMAKE_CUDA_COMPILER_LAUNCHER=ccache
python setup.py develop
If you are editing a single file and rebuilding in a tight loop, the time spent
linking will dominate. The system linker available in most Linux distributions
(GNU ld
) is quite slow. Use a faster linker, like lld.
People on Mac, follow this guide instead.
The easiest way to use lld
this is download the
latest LLVM binaries and run:
ln -s /path/to/downloaded/ld.lld /usr/local/bin/ld
Sometimes there's no way of getting around rebuilding lots of files, for example
editing native_functions.yaml
usually means 1000+ files being rebuilt. If
you're using CMake newer than 3.16, you can enable pre-compiled headers by
setting USE_PRECOMPILED_HEADERS=1
either on first setup, or in the
CMakeCache.txt
file.
USE_PRECOMPILED_HEADERS=1 python setup.py develop
This adds a build step where the compiler takes <ATen/ATen.h>
and essentially
dumps it's internal AST to a file so the compiler can avoid repeating itself for
every .cpp
file.
One caveat is that when enabled, this header gets included in every file by default. Which may change what code is legal, for example:
- internal functions can never alias existing names in
<ATen/ATen.h>
- names in
<ATen/ATen.h>
will work even if you don't explicitly include it.
If re-building without modifying any files results in several CUDA files being
re-compiled, you may be running into an nvcc
bug where header dependencies are
not converted to absolute paths before reporting it to the build system. This
makes ninja
think one of the header files has been deleted, so it runs the
build again.
A compiler-wrapper to fix this is provided in tools/nvcc_fix_deps.py
. You can use
this as a compiler launcher, similar to ccache
export CMAKE_CUDA_COMPILER_LAUNCHER="python;`pwd`/tools/nvcc_fix_deps.py;ccache"
python setup.py develop
We have very extensive tests in the test/cpp/api folder. The
tests are a great way to see how certain components are intended to be used.
When compiling PyTorch from source, the test runner binary will be written to
build/bin/test_api
. The tests use the GoogleTest
framework, which you can read up about to learn how to configure the test runner. When
submitting a new feature, we care very much that you write appropriate tests.
Please follow the lead of the other tests to see how to write a new test case.
If you are debugging pytorch inside GDB, you might be interested in
pytorch-gdb. This script introduces some
pytorch-specific commands which you can use from the GDB prompt. In
particular, torch-tensor-repr
prints a human-readable repr of an at::Tensor
object. Example of usage:
$ gdb python
GNU gdb (GDB) 9.2
[...]
(gdb) # insert a breakpoint when we call .neg()
(gdb) break at::Tensor::neg
Function "at::Tensor::neg" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (at::Tensor::neg) pending.
(gdb) run
[...]
>>> import torch
>>> t = torch.tensor([1, 2, 3, 4], dtype=torch.float64)
>>> t
tensor([1., 2., 3., 4.], dtype=torch.float64)
>>> t.neg()
Thread 1 "python" hit Breakpoint 1, at::Tensor::neg (this=0x7ffb118a9c88) at aten/src/ATen/core/TensorBody.h:3295
3295 inline at::Tensor Tensor::neg() const {
(gdb) # the default repr of 'this' is not very useful
(gdb) p this
$1 = (const at::Tensor * const) 0x7ffb118a9c88
(gdb) p *this
$2 = {impl_ = {target_ = 0x55629b5cd330}}
(gdb) torch-tensor-repr *this
Python-level repr of *this:
tensor([1., 2., 3., 4.], dtype=torch.float64)
GDB tries to automatically load pytorch-gdb
thanks to the
.gdbinit at the root of the pytorch repo. However, auto-loadings is disabled by default, because of security reasons:
$ gdb
warning: File "/path/to/pytorch/.gdbinit" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To enable execution of this file add
add-auto-load-safe-path /path/to/pytorch/.gdbinit
line to your configuration file "/home/YOUR-USERNAME/.gdbinit".
To completely disable this security protection add
set auto-load safe-path /
line to your configuration file "/home/YOUR-USERNAME/.gdbinit".
For more information about this security protection see the
"Auto-loading safe path" section in the GDB manual. E.g., run from the shell:
info "(gdb)Auto-loading safe path"
(gdb)
As gdb itself suggests, the best way to enable auto-loading of pytorch-gdb
is to add the following line to your ~/.gdbinit
(i.e., the .gdbinit
file
which is in your home directory, not /path/to/pytorch/.gdbinit
):
add-auto-load-safe-path /path/to/pytorch/.gdbinit
Set TORCH_SHOW_CPP_STACKTRACES=1
to get the C++ stacktrace when an error occurs in Python.
If you are working on the CUDA code, here are some useful CUDA debugging tips:
CUDA_DEVICE_DEBUG=1
will enable CUDA device function debug symbols (-g -G
). This will be particularly helpful in debugging device code. However, it will slow down the build process for about 50% (compared to onlyDEBUG=1
), so use wisely.cuda-gdb
andcuda-memcheck
are your best CUDA debugging friends. Unlikegdb
,cuda-gdb
can display actual values in a CUDA tensor (rather than all zeros).- CUDA supports a lot of C++11/14 features such as,
std::numeric_limits
,std::nextafter
,std::tuple
etc. in device code. Many of such features are possible because of the --expt-relaxed-constexpr nvcc flag. There is a known issue that ROCm errors out on device code, which uses such stl functions. - A good performance metric for a CUDA kernel is the
Effective Memory Bandwidth.
It is useful for you to measure this metric whenever you are writing/optimizing a CUDA
kernel. Following script shows how we can measure the effective bandwidth of CUDA
uniform_
kernel.import torch from torch.utils.benchmark import Timer size = 128*512 nrep = 100 nbytes_read_write = 4 # this is number of bytes read + written by a kernel. Change this to fit your kernel. for i in range(10): a=torch.empty(size).cuda().uniform_() torch.cuda.synchronize() out = a.uniform_() torch.cuda.synchronize() t = Timer(stmt="a.uniform_()", globals=globals()) res = t.blocked_autorange() timec = res.median print("uniform, size, elements", size, "forward", timec, "bandwidth (GB/s)", size*(nbytes_read_write)*1e-9/timec) size *=2
See more cuda development tips here
For building from source on Windows, consult our documentation on it.
Occasionally, you will write a patch which works on Linux, but fails CI on Windows. There are a few aspects in which MSVC (the Windows compiler toolchain we use) is stricter than Linux, which are worth keeping in mind when fixing these problems.
-
Symbols are NOT exported by default on Windows; instead, you have to explicitly mark a symbol as exported/imported in a header file with
__declspec(dllexport)
/__declspec(dllimport)
. We have codified this pattern into a set of macros which follow the convention*_API
, e.g.,TORCH_API
inside Caffe2, Aten and Torch. (Every separate shared library needs a unique macro name, because symbol visibility is on a per shared library basis. See c10/macros/Macros.h for more details.)The upshot is if you see an "unresolved external" error in your Windows build, this is probably because you forgot to mark a function with
*_API
. However, there is one important counterexample to this principle: if you want a templated function to be instantiated at the call site, do NOT mark it with*_API
(if you do mark it, you'll have to explicitly instantiate all of the specializations used by the call sites.) -
If you link against a library, this does not make its dependencies transitively visible. You must explicitly specify a link dependency against every library whose symbols you use. (This is different from Linux where in most environments, transitive dependencies can be used to fulfill unresolved symbols.)
-
If you have a Windows box (we have a few on EC2 which you can request access to) and you want to run the build, the easiest way is to just run
.ci/pytorch/win-build.sh
. If you need to rebuild, runREBUILD=1 .ci/pytorch/win-build.sh
(this will avoid blowing away your Conda environment.)
Even if you don't know anything about MSVC, you can use cmake to build simple programs on Windows; this can be helpful if you want to learn more about some peculiar linking behavior by reproducing it on a small example. Here's a simple example cmake file that defines two dynamic libraries, one linking with the other:
project(myproject CXX)
set(CMAKE_CXX_STANDARD 14)
add_library(foo SHARED foo.cpp)
add_library(bar SHARED bar.cpp)
# NB: don't forget to __declspec(dllexport) at least one symbol from foo,
# otherwise foo.lib will not be created.
target_link_libraries(bar PUBLIC foo)
You can build it with:
mkdir build
cd build
cmake ..
cmake --build .
The PyTorch codebase sometimes likes to use exciting C++ features, and these exciting features lead to exciting bugs in Windows compilers. To add insult to injury, the error messages will often not tell you which line of code actually induced the erroring template instantiation.
We've found the most effective way to debug these problems is to carefully read over diffs, keeping in mind known bugs in MSVC/NVCC. Here are a few well known pitfalls and workarounds:
-
This is not actually a bug per se, but in general, code generated by MSVC is more sensitive to memory errors; you may have written some code that does a use-after-free or stack overflows; on Linux the code might work, but on Windows your program will crash. ASAN may not catch all of these problems: stay vigilant to the possibility that your crash is due to a real memory problem.
-
(NVCC)
c10::optional
does not work when used from device code. Don't use it from kernels. Upstream issue: akrzemi1/Optional#58 and our local issue #10329. -
constexpr
generally works less well on MSVC.- The idiom
static_assert(f() == f())
to test iff
is constexpr does not work; you'll get "error C2131: expression did not evaluate to a constant". Don't use these asserts on Windows. (Example:c10/util/intrusive_ptr.h
)
- The idiom
-
(NVCC) Code you access inside a
static_assert
will eagerly be evaluated as if it were device code, and so you might get an error that the code is "not accessible".
class A {
static A singleton_;
static constexpr inline A* singleton() {
return &singleton_;
}
};
static_assert(std::is_same(A*, decltype(A::singleton()))::value, "hmm");
-
The compiler will run out of heap space if you attempt to compile files that are too large. Splitting such files into separate files helps. (Example:
THTensorMath
,THTensorMoreMath
,THTensorEvenMoreMath
.) -
MSVC's preprocessor (but not the standard compiler) has a bug where it incorrectly tokenizes raw string literals, ending when it sees a
"
. This causes preprocessor tokens inside the literal like an#endif
to be incorrectly treated as preprocessor directives. See https://godbolt.org/z/eVTIJq as an example. -
Either MSVC or the Windows headers have a PURE macro defined and will replace any occurrences of the PURE token in code with an empty string. This is why we have AliasAnalysisKind::PURE_FUNCTION and not AliasAnalysisKind::PURE. The same is likely true for other identifiers that we just didn't try to use yet.
CUDA, MSVC, and PyTorch versions are interdependent; please install matching versions from this table:
CUDA version | Newest supported VS version | PyTorch version |
---|---|---|
10.1 | Visual Studio 2019 (16.X) (_MSC_VER < 1930) |
1.3.0 ~ 1.7.0 |
10.2 | Visual Studio 2019 (16.X) (_MSC_VER < 1930) |
1.5.0 ~ 1.7.0 |
11.0 | Visual Studio 2019 (16.X) (_MSC_VER < 1930) |
1.7.0 |
Note: There's a compilation issue in several Visual Studio 2019 versions since 16.7.1, so please make sure your Visual Studio 2019 version is not in 16.7.1 ~ 16.7.5
Clang-Tidy is a C++
linter and static analysis tool based on the clang compiler. We run clang-tidy
in our CI to make sure that new C++ code is safe, sane and efficient. See the
clang-tidy
job in our GitHub Workflow's
lint.yml file
for the simple commands we use for this.
To run clang-tidy locally, follow these steps:
- Install clang-tidy. We provide custom built binaries which have additional checks enabled. You can install it by running:
python3 -m tools.linter.install.clang_tidy
We currently only support Linux and MacOS (x86).
- Install clang-tidy driver script dependencies
pip3 install -r tools/linter/clang_tidy/requirements.txt
- Run clang-tidy
# Run clang-tidy on the entire codebase
make clang-tidy
# Run clang-tidy only on your changes
make clang-tidy CHANGED_ONLY=--changed-only
This internally invokes our driver script and closely mimics how clang-tidy is run on CI.
We use clang-tidy to perform additional formatting and semantic checking of code. We provide a pre-commit git hook for performing these checks, before a commit is created:
ln -s ../../tools/git-pre-commit .git/hooks/pre-commit
If you have already committed files and
CI reports flake8
errors, you can run the check locally in your PR branch with:
flake8 $(git diff --name-only $(git merge-base --fork-point main))
You'll need to install an appropriately configured flake8; see Lint as you type for documentation on how to do this.
Fix the code so that no errors are reported when you re-run the above check again, and then commit the fix.
ASAN is very useful for debugging memory errors in C++. We run it in CI, but here's how to get the same thing to run on your local machine.
First, install LLVM 8. The easiest way is to get prebuilt
binaries and extract them to
folder (later called $LLVM_ROOT
).
Then set up the appropriate scripts. You can put this in your .bashrc
:
LLVM_ROOT=<wherever your llvm install is>
PYTORCH_ROOT=<wherever your pytorch checkout is>
LIBASAN_RT="$LLVM_ROOT/lib/clang/8.0.0/lib/linux/libclang_rt.asan-x86_64.so"
build_with_asan()
{
LD_PRELOAD=${LIBASAN_RT} \
CC="$LLVM_ROOT/bin/clang" \
CXX="$LLVM_ROOT/bin/clang++" \
LDSHARED="clang --shared" \
LDFLAGS="-stdlib=libstdc++" \
CFLAGS="-fsanitize=address -fno-sanitize-recover=all -shared-libasan -pthread" \
CXX_FLAGS="-pthread" \
USE_CUDA=0 USE_OPENMP=0 BUILD_CAFFE2_OPS=0 USE_DISTRIBUTED=0 DEBUG=1 \
python setup.py develop
}
run_with_asan()
{
LD_PRELOAD=${LIBASAN_RT} $@
}
# you can look at build-asan.sh to find the latest options the CI uses
export ASAN_OPTIONS=detect_leaks=0:symbolize=1:strict_init_order=true
export UBSAN_OPTIONS=print_stacktrace=1:suppressions=$PYTORCH_ROOT/ubsan.supp
export ASAN_SYMBOLIZER_PATH=$LLVM_ROOT/bin/llvm-symbolizer
Then you can use the scripts like:
suo-devfair ~/pytorch ❯ build_with_asan
suo-devfair ~/pytorch ❯ run_with_asan python test/test_jit.py
The scripts above specify the clang
and clang++
binaries directly, which
bypasses ccache
. Here's how to get ccache
to work:
- Make sure the ccache symlinks for
clang
andclang++
are set up (see CONTRIBUTING.md) - Make sure
$LLVM_ROOT/bin
is available on your$PATH
. - Change the
CC
andCXX
variables inbuild_with_asan()
to point directly toclang
andclang++
.
The “standard” workflow for ASAN assumes you have a standalone binary:
- Recompile your binary with
-fsanitize=address
. - Run the binary, and ASAN will report whatever errors it find.
Unfortunately, PyTorch is a distributed as a shared library that is loaded by a third-party executable (Python). It’s too much of a hassle to recompile all of Python every time we want to use ASAN. Luckily, the ASAN folks have a workaround for cases like this:
- Recompile your library with
-fsanitize=address -shared-libasan
. The extra-shared-libasan
tells the compiler to ask for the shared ASAN runtime library. - Use
LD_PRELOAD
to tell the dynamic linker to load the ASAN runtime library before anything else.
More information can be found here.
We need LD_PRELOAD
because there is a cmake check that ensures that a
simple program builds and runs. If we are building with ASAN as a shared
library, we need to LD_PRELOAD
the runtime library, otherwise there will
dynamic linker errors and the check will fail.
We don’t actually need either of these if we fix the cmake checks.
Python leaks a lot of memory. Possibly we could configure a suppression file, but we haven’t gotten around to it.
In 2018, we merged Caffe2 into the PyTorch source repository. While the steady state aspiration is that Caffe2 and PyTorch share code freely, in the meantime there will be some separation.
There are a few "unusual" directories which, for historical reasons, are Caffe2/PyTorch specific. Here they are:
-
CMakeLists.txt
,Makefile
,binaries
,cmake
,conda
,modules
,scripts
are Caffe2-specific. Don't put PyTorch code in them without extra coordination. -
mypy*
,requirements.txt
,setup.py
,test
,tools
are PyTorch-specific. Don't put Caffe2 code in them without extra coordination.
Once you submit a PR or push a new commit to a branch that is in an active PR, CI jobs will be run automatically. Some of these may fail and you will need to find out why, by looking at the logs.
Fairly often, a CI failure might be unrelated to your changes. You can confirm by going to our HUD and seeing if the CI job is failing upstream already. In this case, you can usually ignore the failure. See the following subsection for more details.
Some failures might be related to specific hardware or environment configurations. In this case, if you're a Meta employee, you can ssh into the job's session to perform manual debugging following the instructions in our CI wiki.
For CI run on main
, this repository is checked out for a given main
commit, and CI is run on that commit (there isn't really any other choice).
For PRs, however, it's a bit more complicated. Consider this commit graph, where
main
is at commit A
, and the branch for PR #42 (just a placeholder) is at
commit B
:
o---o---B (refs/pull/42/head)
/ \
/ C (refs/pull/42/merge)
/ /
---o---o---o---A (merge-destination) - usually main
There are two possible choices for which commit to use:
- Checkout commit
B
, the head of the PR (manually committed by the PR author). - Checkout commit
C
, the hypothetical result of what would happen if the PR were merged into it's destination (usuallymain
).
For all practical purposes, most people can think of the commit being used as
commit B
(choice 1).
However, if workflow files (which govern CI behavior) were modified (either by your PR or since dev branch were created ) there's
a nuance to know about:
The workflow files themselves get taken from checkpoint C
, the merger of your
PR and the main
branch. But only the workflow files get taken from that merged
checkpoint. Everything else (tests, code, etc) all get taken directly from your
PR's commit (commit B
). Please note, this scenario would never affect PRs authored by ghstack
as they would not automatically ingest the updates from default branch.
Dev Infra Office Hours are hosted every Friday to answer any questions regarding developer experience, Green HUD, and CI.