ONNX Support

Vollo also provides a tool for compiling ML models defined in ONNX.

vollo-onnx is a command line tool which allows the user to specify an input ONNX file and produces a .vollo program as output. The user specifies a path to the input .onnx file:

Arguments:
  <INPUT>
          Path to the input .onnx file

The user can specify:

• The output path:

  -o, --output <OUTPUT>
        Output path for the compiled program file
  
        [default: program.vollo]
  

• The hardware configuration to use (this JSON file can be generated using the Config method save in vollo_compiler):

      --hw-config <HW_CONFIG_JSON>
        Path to the hardware config JSON file
  
        If unspecified, defaults to the 6 core block size 32 IA_420F configuration
  

• Which transformations to perform on the model (see Example 2: Batched MLP for the unweaving transform and Example 3: CNN for the streaming transform):

  --streaming-transform <STREAMING_AXIS>
        Axis on which to perform the streaming transform in the NNIR graph
  
        If unspecified, no streaming transform is performed
  
  --unweave
        Perform the unweaving transform
  

• The input shape of the model. This is required if the ONNX model has dynamic input shapes. Vollo requires that the shape of the input be known at compile-time:

  --override-input-shape <SHAPE>
        If the model has dynamic input shapes, the user must pass a fixed input shape
  
        Example: 10,100,250
  

Simplifying ONNX Models

vollo-onnx has a limited list of supported ONNX nodes. Often ONNX models can be over-complicated, and contain unnecessary shaping operations. It is recommended that onnx-simplifier be used before calling vollo-onnx on an ONNX model to remove these unnecessary shaping operations which aren't supported by vollo-onnx:

onnx-sim <model.onnx> <model-sim.onnx> --overwrite-input-shape <model-input-shape>

It is also recommended to use the --overwrite-input-shape with onnx-simplifier, as this can enable further simplifications and better constant folding.

Using ONNX from Python

ONNX models can also be imported and translated to NNIR models directly in python using the static NNIR method from_onnx. This also requires that the input shape be specified if the ONNX model has dynamic input shapes, otherwise it can be None.

onnx_nnir = vollo_compiler.NNIR.from_onnx(onnx_path, input_shape)

Supported Nodes

Tensors are expected to be in float32 format, unless they are used as indices / axes (in which case they should be int64s).

vollo-onnx supports models with the following nodes: