9e8d795344
* Update ORT Mobile documentation for both the pre-built package and custom build usage Add info on pre-built package and CoreML EP Refer to operator kernels and contrib ops documentation in github so we can point to the version specific content Tweak some aspects like not specifying nav_order in places (items sort alphabetically by default) * merge previous unmerged ios doc updates * Address PR comments * Minor tweaks * Address PR comments Co-authored-by: Guoyu Wang <wanggy@outlook.com>
2.9 KiB
| title | parent | grand_parent |
|---|---|---|
| NNAPI | Execution Providers | Reference |
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NNAPI Execution Provider
Android Neural Networks API (NNAPI) is a unified interface to CPU, GPU, and NN accelerators on Android.
Contents
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Requirements
The NNAPI Execution Provider (EP) requires Android devices with Android 8.1 or higher. It is recommended to use Android devices with Android 9 or higher to achieve optimal performance.
Build
Please see the ONNX Runtime Mobile deployment information for instructions on building or using a pre-built package that includes the NNAPI EP.
Usage
The ONNX Runtime API details are here.
The NNAPI EP can be used via the C, C++ or Java APIs
The NNAPI EP must be explicitly registered when creating the inference session. For example:
Ort::Env env = Ort::Env{ORT_LOGGING_LEVEL_ERROR, "Default"};
Ort::SessionOptions so;
uint32_t nnapi_flags = 0;
Ort::ThrowOnError(OrtSessionOptionsAppendExecutionProvider_Nnapi(so, nnapi_flags));
Ort::Session session(env, model_path, so);
Configuration Options
There are several run time options available for the NNAPI EP.
To use the NNAPI EP run time options, create an unsigned integer representing the options, and set each individual option by using the bitwise OR operator.
uint32_t nnapi_flags = 0;
nnapi_flags |= NNAPI_FLAG_USE_FP16;
Available Options
NNAPI_FLAG_USE_FP16
Use fp16 relaxation in NNAPI EP.
This may improve performance but can also reduce accuracy due to the lower precision.
NNAPI_FLAG_USE_NCHW
Use the NCHW layout in NNAPI EP.
This is only available for Android API level 29 and later. Please note that for now, NNAPI might have worse performance using NCHW compared to using NHWC.
NNAPI_FLAG_CPU_DISABLED
Prevent NNAPI from using CPU devices.
NNAPI is more efficient using GPU or NPU for execution, however NNAPI might fall back to its CPU implementation for operations that are not supported by GPU/NPU. The CPU implementation of NNAPI (which is called nnapi-reference) is often less efficient than the optimized versions of the operation of ORT. Due to this, it may be advantageous to disable the NNAPI CPU fallback and handle execution using ORT kernels.
For some models, if NNAPI would use CPU to execute an operation, and this flag is set, the execution of the model may fall back to ORT kernels.
This option is only available after Android API level 29, and will be ignored for Android API level 28 and lower.
For NNAPI device assignments, see https://developer.android.com/ndk/guides/neuralnetworks#device-assignment
For NNAPI CPU fallback, see https://developer.android.com/ndk/guides/neuralnetworks#cpu-fallback