InfMoE

Inference framework for MoE-based models, based on a TensorRT custom plugin named MoELayerPlugin (including Python binding) that can run inference of MoE layers with any sub-layer on NVIDIA GPUs with minimal memory consumption.

InfMoE is open-sourced under MIT License.

Installation

Dependencies:

• CUDA (>=10.2)
• cuDNN (>=8.0, corresponding to CUDA version)
• TensorRT (>=7.0, corresponding to CUDA & cuDNN version)
• zlib (to read npz files)
• meson & ninja (building system)

Python (recommended)

To use TensorRT in Python, you need to first install:

• TensorRT pip package (either from downloaded TensorRT package or from PyPI as nvidia-tensorrt, see https://docs.nvidia.com/deeplearning/tensorrt/install-guide/index.html#installing-pip)
• PyCUDA

Simply you could run python3 -m pip install -r requirements.txt.

Note: If you install nvidia-tensorrt from PyPI (but not from downloaded TensorRT package), you MUST ensure the version of TensorRT that MoELayerPlugin links to matches the version that pip package uses (see site-packages/tensorrt/). Otherwise the plugin will not work correctly.

Then build this plugin:

cd python

# if you have cuDNN & TensorRT installed in search path, or
python3 setup.py build_ext
# if you need to specify CUDA / cuDNN install location
# (CUDA can only be automatically searched by meson)
python3 setup.py build_ext --tensorrt-prefix=/path/to/tensorrt --cudnn-prefix=/path/to/cudnn

python3 setup.py install .

You can also use bdist_wheel or other commands provided by setuptools. You can pass --debug to build_ext to enable verbose logging & keep the symbols for debugging purpose.

C++ only (advanced)

cd plugin

# if you have cuDNN & TensorRT installed in search path
make builddir && make compile

# if you need to specify CUDA / cuDNN install location
# (CUDA can only be automatically searched by meson)
meson setup build -DWITH_TENSORRT=/path/to/tensorrt -DWITH_CUDNN=/path/to/cudnn
ninja -C builddir # or just run `make`

If everything goes well, you can find libtrtmoelayer.so in builddir. Similarly you can pass -DDEBUG=true to meson setup for debugging.

Plugin attributes

When initializing MoELayerPlugin in TensorRT (either C++ or Python), the following attributes must be specified:

• expert_count: INT32, number of experts (sub-layers)
• embedding_size: INT32, the input & output size of expert network
• hidden_size: INT32, the intermediate size of feed forward network (might not be used by sub-layer)
• max_concurrency: INT32, maximal concurrent experts in GPU memory (default to 2), setting it too large will lead to OOM
• expert_centroids: FLOAT32 array, weight for dispatching tokens to experts, must be shape (d_model, expert_count) where d_model is the last dimension of input tensor (a.k.a. embedding size)
• expert_weight_file: null-terminated CHAR array, path to expert weight file, to be read by implmentation of sub-layer
• expert_sublayer_type: null-terminated CHAR array, type of sub-layer used, currently only T5_FF can be used
• moe_variant: null-terminated CHAR array, variant type of MoE layer, used to decide different behaviours (can be cpm_2, base_layer or default)
• layernorm_weight: FLOAT32 array, weight of layer norm layer applied to input before calculating expert affliation / score, must be provided when moe_variant is cpm_2

Usage

Currently InfMoE can only handle MoE layers with FP32 parameters, input & output. To run inference with a full network, you should slice it before and after any MoE layer:

• For non-MoE layers, jsut save them as onnx / UFF format and use TensorRT to parse it into a network (Python / C++). Or you can use TensorRT API to construct the network manually (Python / C++).
• For MoE layers, dump expert centroids and weights of each expert separately (in the format mentioned below), create a layer using MoELayerPlugin with Python or C++ (see examples).

Then you can concatenate MoE / non-MoE layers to obtain the full network (or replace any specific 'placeholder' layer with MoE layer), which can be later built into a TensorRT CUDA engine and used to run inference with / serialize & dump to file.

We provide several Python examples in python/examples showing how to do the aforementioned work. You can run them after installing this plugin. You are encouraged to read TensorRT documentation to understand its workflow prior to using this plugin.

Error handling

InfMoE requires that none of the following tensors contains NaN values:

• layer input
• expert centroids
• weight of layer norm (if applicable)

It will also check the shape and data type of all parameters, input & output tensors. If any misconfiguration is found, it will print error message to stderr and abort the whole process.

Scheduling

See CPM-2 paper for scheduling details. To be ported to public source code soon.

Sub-layer

We have provided some sublayers in plugin/sublayers. To implement your own sub-layer, you need to:

• Extend MoESubLayer class
• Add your layer name and initialization code to MoELayerPlugin.h (in sublayer_type) and MoELayerPlugin.cc (in MoELayerPlugin::createSublayer())
• Add your source file (.cpp only) to meson.build
• Rebuild the plugin

T5FFLayer (T5_FF)

This project includes an sublayer implementation of feed-forward layer in T5 network. It is defined as:

hs := hs + dense_relu_dense(layer_norm(hs))
layer_norm(hs) := wl * hs / sqrt(mean(pow(hs, 2)) + eps)
dense_relu_dense(hs) := (gelu(hs @ wi_0^T) * (hs @ wi_1^T)) @ wo^T

where wi_0, wi_1 and wo are linear layers with no bias, first converting input tensor to 4 times large (in last dimension) then back.

The given export_weight_file must be a npz file containing the following variables (n varies from 0 to expert_count - 1): n/layer_norm_weight, n/wi_0_weight, n/wi_1_weight, n/wo_weight.

IdentityLayer (Identity)

This layer DOES NOTHING (thus use none of the provided plugin attributes), just copies the input directly to the output. It is intended for debugging purpose only.