[Adreno] Add documentation for Adreno deployment (apache#13393)

* [Adreno] Add documentation for Adreno deployment
Purpose:
assist TVM users compile and deploy on Adreno by expanding our documentation and providing sample scripts in TVM.

Information about PR:
The present PR consists globally of 3 parts.

The first part is an introductory article on compilation and deployment of neural networks on Adreno, covering such topics as: «Build TVM for Android/Adreno», «Advantages of textures» and «Differences in compilation and deployment of models for Adreno devices».

The second part is a straightforward example script for compiling and inferring models at different precisions for Adreno devices.

The third part is auxiliary files, images, etc.

* Add correct links to images + small fixes

* Remove images (.png)

* Add request_hook in deploy_model_on_adreno.py

* Fix trailing newline + add license

* No newline at the EOF + blanks

* Fix request hook placing

* Fix style

* Fix trailing

* Fix whitespaces

* Fix whitespaces v2

* Add newline at adreno.rst EOF

* Add license to adreno.rst

* Remove sphinx 'autosectionlabel' extension + modify cross-references in docs to work without this extension

* Set default values to tracker_host and tracker_port

* Add local_demo to be able to autogenerate docs

* Fix quotes

* Fix benchmark

* .

docs/how_to/deploy/adreno.rst

@@ -0,0 +1,336 @@
+..  Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+..    http://www.apache.org/licenses/LICENSE-2.0
+
+..  Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+
+Deploy to Adreno GPU
+=======================================
+
+**Authors**: Daniil Barinov, Egor Churaev, Andrey Malyshev
+
+Introduction
+------------
+
+Adreno is a series of graphics processing unit (GPU) semiconductor
+intellectual property cores developed by Qualcomm and used in many of
+their SoCs.
+
+The Adreno GPU accelerates the rendering of complex geometries to
+deliver high-performance graphics and a rich user experience with low
+power consumption.
+
+This guide will demonstrate :ref:`the benefits of using textures with Adreno<advantages_of_the_textures>`,
+how to :ref:`build TVM with OpenCL<building_tvm_for_adreno>` (needed by Adreno devices) and TVM RPC
+enabled. It will also provide :ref:`example code<build_and_deploy_model_for_adreno>` to better understand the differences in compiling and deploying models
+for Adreno devices.
+
+.. _advantages_of_the_textures:
+
+Advantages of the Textures
+--------------------------
+
+One of the Adreno's advantages is the clever handling of textures. At
+the moment, TVM is able to benefit from this by having texture support
+for Adreno. The graph below shows the Adreno A5x architecture.
+
+|High-level overview of the Adreno A5x architecture for OpenCL|
+
+*Fig. 1 High-level overview of the Adreno A5x architecture for OpenCL*
+
+*source:* `OpenCL Optimization and Best Practices for Qualcomm Adreno GPUs <https://dl.acm.org/doi/10.1145/3204919.3204935>`_
+
+Reasons of using textures:
+
+-  Texture processor (TP) has a dedicated L1 cache, which is read-only cache and stores data
+   fetched from level-2 (L2) cache for texture operations (primary
+   reason)
+
+-  The handling of image boundaries is built-in.
+
+-  Supports numerous image format and data type combinations with
+   support for automatic format conversions
+
+Overall, with textures, it is possible to achieve a significant performance boost
+compared to OpenCL buffer based solutions.
+
+.. _building_tvm_for_adreno:
+
+Building TVM for Adreno
+-----------------------
+
+This section gives instructions on how to build the Android part of TVM
+with OpenCL and TVM RPC Server in order to deploy models on Adreno.
+
+Since the process of building TVM for Adreno is exactly the same as the
+process of building TVM for Android, please refer to these instructions:
+`TVM RPC
+Server <https://github.com/apache/tvm/tree/main/apps/cpp_rpc>`_.
+
+Since there are many required packages for Android, you can use the official Docker Image to build TVM.
+For more information refer to this guide: `Deploy the Pretrained Model on Android <https://tvm.apache.org/docs/how_to/deploy_models/deploy_model_on_android.html>`_.
+
+**Prerequisites**: Android NDK and Android Debug Bridge must
+be installed, the desired device must have OpenCL support and Android part of TVM must be built:
+
+- Read documentation about *Android NDK installation* here: https://developer.android.com/ndk
+- To get access to adb tools you can see *Android Debug Bridge installation* here: https://developer.android.com/studio/command-line/adb
+
+You can also build the android part of TVM locally. From the root
+folder of TVM:
+
+::
+
+   mkdir build_android
+   cd build_android
+   cmake .. -DUSE_OPENCL=ON -DUSE_MICRO=OFF -DCMAKE_TOOLCHAIN_FILE=${ANDROID_NDK_HOME}/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a -DANDROID_NATIVE_API_LEVEL=android-28 -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ON -DANDROID_STL=c++_static -DUSE_CPP_RPC=ON
+   make -jN tvm_runtime tvm_rpc
+
+where **N** is the number of cores available on your *CPU*.
+
+At this stage you have built TVM for Adreno.
+
+.. _build_and_deploy_model_for_adreno:
+
+Build and deploy model for Adreno
+---------------------------------
+
+In this section we will focus on target, needed to compile and deploy models for Adreno, demonstrate
+the differences in generated kernels with and without textures and, in addition, the
+possibility of choosing a different precision for model compilation will
+be considered.
+
+For the complete step-py-step process of compiling and deploying models on
+Adreno, including selection of precision, running the inference of the
+model, getting the predictions, and measuring the performance please refer to this tutorial: `How To Deploy model on Adreno <https://tvm.apache.org/docs/how_to/deploy_models/deploy_model_on_adreno.html>`_
+
+|Android deployment pipeline|
+
+*Fig.2 Deployment pipeline on Adreno devices*
+
+The figure above demonstrates a generalized pipeline for deploying and running neural network models on android devices.
+As can be seen from the figure, the compiled model has a set_input() and a run() methods,
+which *prepare the inputs* for inference and *execute the inference* on the remote device using the Graph Executor runtime module.
+
+Adreno target
+~~~~~~~~~~~~~
+
+Normally, when compiling models for Android using OpenCL, the
+corresponding target is used
+
+.. code:: python
+
+   target="opencl"
+
+Using Adreno, we want to get all the benefits of textures, so we have to
+use the following target to generate texture leveraging kernels
+
+.. code:: python
+
+   target="opencl -device=adreno"
+
+Let's write a simple model with one convolutional (conv2d) layer and take a look at generated kernels for these
+two targets
+
+.. code:: python
+
+   import tvm
+   from tvm import relay
+   import numpy as np
+
+   input_shape=(1, 56, 56, 32)
+   filter_shape=(3, 3, 32, 64)
+   filter = np.random.rand(*filter_shape)
+
+   dtype="float32"
+   input = tvm.relay.var("input", shape=input_shape, dtype=dtype)
+   weight = tvm.relay.var("weight", shape=filter_shape, dtype=dtype)
+   D = relay.nn.conv2d(input, weight, padding=(1, 1), data_layout="NHWC", kernel_layout="HWIO", out_dtype=dtype)
+
+   mod = relay.Function([input, weight], D)
+   params = {
+      "weight": tvm.nd.array(filter)
+   }
+
+Now compile our model with the classic OpenCL target and print its modules:
+
+.. code:: python
+
+   target="opencl"
+
+   with tvm.transform.PassContext(opt_level=3):
+      graph, lib, params = relay.build_module.build(mod, target, params=params)
+   print(lib.imported_modules[0].get_source())
+
+Notice that the generated convolution kernel has pointers in
+the initialization of the function. The kernels generated with the above target are buffer-based.
+
+.. code:: c
+
+   __kernel void tvmgen_default_fused_nn_conv2d_kernel0(__global float* restrict p0, __global double* restrict p1, __global float* restrict conv2d_nhwc) {
+   // body..
+
+
+Now take a look at “opencl -device=adreno” target:
+
+.. code:: python
+
+   target="opencl -device=adreno"
+
+   with tvm.transform.PassContext(opt_level=3):
+      graph, lib, params = relay.build_module.build(mod, target, params=params)
+   print(lib.imported_modules[0].get_source())
+
+The kernels generated this way is actually working with 2d arrays, leveraging textures
+
+.. code:: c
+
+   __kernel void tvmgen_default_fused_nn_conv2d_kernel0(__write_only image2d_t pad_temp_global_texture, __read_only image2d_t p0) {
+   // body..
+
+*image2d_t* is a built-in OpenCL types that represents two-dimensional image object and provides several additional functions.
+When we use *image2d_t* we read *4 elements at one time*, and it helps to utilize hardware in a more efficient way.
+
+Precisions
+~~~~~~~~~~
+The right choice of precision for a specific workload can greatly increase the efficiency of the solution,
+shifting the initial balance of precision and speed to the side that is a priority for the problem.
+
+We can choose from *float16*, *float16_acc32* (Mixed Precision), *float32* (standard).
+
+**Float16**
+
+To leverage the GPU hardware capabilities and utilize the benefits of half precision computation and memory management,
+we can convert an original model having floating points operation to a model operating with half precision.
+Choosing lower precision will positively affect the performance of the model, but it may also have a decrease in the accuracy of the model.
+To do the conversion you need to write a simple conversion function and specify the *dtype* value of "float16" before calling the function:
+
+.. code:: python
+
+   def  convert_to_dtype(mod, dtype):
+      # downcast to float16
+      if  dtype == "float16":
+         global  conv2d_acc = "float16"
+         from  tvm.ir  import  IRModule
+         mod = IRModule.from_expr(mod)
+         seq = tvm.transform.Sequential(
+            [
+                  relay.transform.InferType(),
+                  relay.transform.ToMixedPrecision()
+            ]
+         )
+         with  tvm.transform.PassContext(opt_level=3):
+            mod = seq(mod)
+      return  mod
+
+   dtype="float16"
+   mod = convert_to_dtype(mod["main"], dtype)
+
+We then can compile our model in any convinient way
+
+.. code:: python
+
+   with  tvm.transform.PassContext(opt_level=3):
+       lib = relay.build(
+           mod, target_host=target_host, target=target, params=params
+       )
+
+**float16_acc32 (Mixed Precision)**
+
+ToMixedPrecision pass traverse over the network and split network to clusters of ops dealing with float or float16 data types.
+The clusters are defined by three types of operations:
+- Operations always be converted into float16 data type
+- Operations which can be converted if they follow by converted cluster
+- Operations never be converted to the float16 data type
+This list is defined in the ToMixedPrecision implementation here
+`relay/transform/mixed_precision.py <https://github.com/apache/tvm/blob/main/python/tvm/relay/transform/mixed_precision.py#L34>`_
+and can be overridden by user
+
+In some cases, we want higher precision in accumulation than the input data.
+This is supported, for example, for conv2d and dense operations. To override accumulation type you need to register
+function with ``@register_mixed_precision_conversion`` decorator to modify parameters of ``ToMixedPrecision`` conversion
+
+.. code:: python
+
+   from  tvm.relay.op  import  register_mixed_precision_conversion
+
+   conv2d_acc = "float32"
+
+   # Pick a priority > 10 to overwrite defaults, higher priorities take precedence
+   @register_mixed_precision_conversion("nn.conv2d", level=11)
+   def  conv2d_mixed_precision_rule(call_node: "relay.Call", mixed_precision_type: str):
+       global  conv2d_acc
+       return [
+           # always do main calculation in mixed_precision_type
+           relay.transform.mixed_precision.MIXED_PRECISION_ALWAYS,
+           # the dtype for the accumulator
+           conv2d_acc,
+           # the output dtype for the operation (usually fp16)
+           mixed_precision_type,
+       ]
+
+   # Same for dense
+   @register_mixed_precision_conversion("nn.dense", level=11)
+   def  conv2d_mixed_precision_rule(call_node: "relay.Call", mixed_precision_type: str):
+       global  conv2d_acc
+       return [
+           relay.transform.mixed_precision.MIXED_PRECISION_ALWAYS,
+           conv2d_acc,
+           mixed_precision_type,
+       ]
+
+Now we need to modify the conversion function by adding some logical "forks" and ToMixedPrecision() call,
+then create a Relay graph from desired model in any convinient way and obtain **mod** (which is IR representation of the model),
+after which we can convert it to the required **dtype** and then assemble our model sequentialy
+
+.. code:: python
+
+   def  convert_to_dtype(mod, dtype):
+       # downcast to float16
+       if  dtype == "float16"  or  dtype == "float16_acc32":
+           global  conv2d_acc
+           conv2d_acc = "float16"  if  dtype == "float16"  else  "float32"
+           from  tvm.ir  import  IRModule
+           mod = IRModule.from_expr(mod)
+           seq = tvm.transform.Sequential(
+               [
+                   relay.transform.InferType(),
+                   relay.transform.ToMixedPrecision()
+               ]
+           )
+           with tvm.transform.PassContext(
+                config={"relay.ToMixedPrecision.keep_orig_output_dtype": True},
+                opt_level=3):
+            mod = seq(mod)
+       return  mod
+
+   dtype="float16_acc32"
+   mod = convert_to_dtype(mod["main"], dtype)
+   dtype = "float32"  if  dtype == "float32"  else  "float16"
+
+The ``ToMixedPrecision`` method is a pass to convert an FP32 relay graph into an FP16 version (with
+FP16 or FP32 accumulation dtypes). Doing this transformation is useful for reducing model size
+as it halves the expected size of the weights (FP16_acc16 case).
+
+From this point onwards, we can compile our model as normal
+
+.. code:: python
+
+   with  tvm.transform.PassContext(opt_level=3):
+       lib = relay.build(
+           mod, target_host=target_host, target=target, params=params
+       )
+
+.. |High-level overview of the Adreno A5x architecture for OpenCL| image:: https://raw.githubusercontent.com/tlc-pack/web-data/main/images/how-to/adreno_architecture.png
+.. |Android deployment pipeline| image:: https://raw.githubusercontent.com/tlc-pack/web-data/main/images/how-to/android_deployment_pipeline.jpg

docs/how_to/deploy/index.rst

@@ -169,6 +169,7 @@ target device without relying on RPC. See the following resources on how to do s
 
    cpp_deploy
    android
+   adreno
    integrate
    hls
    arm_compute_lib