Add Tutorial of QAT with X86InductorQuantizer (#2717)

* Add QAT Tutorial
---------

Co-authored-by: Svetlana Karslioglu <svekars@meta.com>

Author: leslie-fang-intel

prototype_source/prototype_index.rst

@@ -89,6 +89,12 @@ Prototype features are not available as part of binary distributions like PyPI o
    :link: ../prototype/pt2e_quant_qat.html
    :tags: Quantization
 
+.. customcarditem::
+   :header: PyTorch 2 Export Quantization with X86 Backend through Inductor
+   :card_description: Learn how to use PT2 Export Quantization with X86 Backend through Inductor.
+   :image: ../_static/img/thumbnails/cropped/generic-pytorch-logo.png
+   :link: ../prototype/pt2e_quant_x86_inductor.html
+   :tags: Quantization
 
 .. Sparsity
 

prototype_source/pt2e_quant_ptq_x86_inductor.rst renamed to prototype_source/pt2e_quant_x86_inductor.rst

@@ -1,29 +1,31 @@
-PyTorch 2 Export Post Training Quantization with X86 Backend through Inductor
-========================================================================================
+PyTorch 2 Export Quantization with X86 Backend through Inductor
+==================================================================
 
 **Author**: `Leslie Fang <https://github.com/leslie-fang-intel>`_, `Weiwen Xia <https://github.com/Xia-Weiwen>`_, `Jiong Gong <https://github.com/jgong5>`_, `Jerry Zhang <https://github.com/jerryzh168>`_
 
 Prerequisites
-^^^^^^^^^^^^^^^
+---------------
 
 -  `PyTorch 2 Export Post Training Quantization <https://pytorch.org/tutorials/prototype/pt2e_quant_ptq.html>`_
+-  `PyTorch 2 Export Quantization-Aware Training <https://pytorch.org/tutorials/prototype/pt2e_quant_qat.html>`_
 -  `TorchInductor and torch.compile concepts in PyTorch <https://pytorch.org/tutorials/intermediate/torch_compile_tutorial.html>`_
 -  `Inductor C++ Wrapper concepts <https://pytorch.org/tutorials/prototype/inductor_cpp_wrapper_tutorial.html>`_
 
 Introduction
-^^^^^^^^^^^^^^
+--------------
 
 This tutorial introduces the steps for utilizing the PyTorch 2 Export Quantization flow to generate a quantized model customized
 for the x86 inductor backend and explains how to lower the quantized model into the inductor.
 
-The new quantization 2 flow uses the PT2 Export to capture the model into a graph and perform quantization transformations on top of the ATen graph. This approach is expected to have significantly higher model coverage, better programmability, and a simplified UX.
+The pytorch 2 export quantization flow uses the torch.export to capture the model into a graph and perform quantization transformations on top of the ATen graph.
+This approach is expected to have significantly higher model coverage, better programmability, and a simplified UX.
 TorchInductor is the new compiler backend that compiles the FX Graphs generated by TorchDynamo into optimized C++/Triton kernels.
 
 This flow of quantization 2 with Inductor mainly includes three steps:
 
 - Step 1: Capture the FX Graph from the eager Model based on the `torch export mechanism <https://pytorch.org/docs/main/export.html>`_.
 - Step 2: Apply the Quantization flow based on the captured FX Graph, including defining the backend-specific quantizer, generating the prepared model with observers,
-  performing the prepared model's calibration, and converting the prepared model into the quantized model.
+  performing the prepared model's calibration or quantization-aware training, and converting the prepared model into the quantized model.
 - Step 3: Lower the quantized model into inductor with the API ``torch.compile``.
 
 The high-level architecture of this flow could look like this:
@@ -61,10 +63,14 @@ and outstanding out-of-box performance with the compiler backend. Especially on
 further boost the models' performance by leveraging the
 `advanced-matrix-extensions <https://www.intel.com/content/www/us/en/products/docs/accelerator-engines/advanced-matrix-extensions/overview.html>`_ feature.
 
-Now, we will walk you through a step-by-step tutorial for how to use it with `torchvision resnet18 model <https://download.pytorch.org/models/resnet18-f37072fd.pth>`_.
+Post Training Quantization
+----------------------------
+
+Now, we will walk you through a step-by-step tutorial for how to use it with `torchvision resnet18 model <https://download.pytorch.org/models/resnet18-f37072fd.pth>`_
+for post training quantization.
 
 1. Capture FX Graph
----------------------
+^^^^^^^^^^^^^^^^^^^^^
 
 We will start by performing the necessary imports, capturing the FX Graph from the eager module.
 
@@ -111,7 +117,7 @@ We will start by performing the necessary imports, capturing the FX Graph from t
 Next, we will have the FX Module to be quantized.
 
 2. Apply Quantization
-----------------------------
+^^^^^^^^^^^^^^^^^^^^^^^
 
 After we capture the FX Module to be quantized, we will import the Backend Quantizer for X86 CPU and configure how to
 quantize the model.
@@ -160,7 +166,7 @@ After these steps, we finished running the quantization flow and we will get the
 
 
 3. Lower into Inductor
-------------------------
+^^^^^^^^^^^^^^^^^^^^^^^^
 
 After we get the quantized model, we will further lower it to the inductor backend. The default Inductor wrapper
 generates Python code to invoke both generated kernels and external kernels. Additionally, Inductor supports
@@ -222,8 +228,74 @@ With PyTorch 2.1 release, all CNN models from TorchBench test suite have been me
 to `this document <https://dev-discuss.pytorch.org/t/torchinductor-update-6-cpu-backend-performance-update-and-new-features-in-pytorch-2-1/1514#int8-inference-with-post-training-static-quantization-3>`_
 for detail benchmark number.
 
-4. Conclusion
----------------
+Quantization Aware Training
+-----------------------------
+
+The PyTorch 2 Export Quantization-Aware Training (QAT) is now supported on X86 CPU using X86InductorQuantizer,
+followed by the subsequent lowering of the quantized model into Inductor.
+For a more in-depth understanding of PT2 Export Quantization-Aware Training,
+we recommend referring to the dedicated `PyTorch 2 Export Quantization-Aware Training <https://pytorch.org/tutorials/prototype/pt2e_quant_qat.html>`_.
+
+The PyTorch 2 Export QAT flow is largely similar to the PTQ flow:
+
+.. code:: python
+
+  import torch
+  from torch._export import capture_pre_autograd_graph
+  from torch.ao.quantization.quantize_pt2e import (
+    prepare_qat_pt2e,
+    convert_pt2e,
+  )
+  import torch.ao.quantization.quantizer.x86_inductor_quantizer as xiq
+  from torch.ao.quantization.quantizer.x86_inductor_quantizer import X86InductorQuantizer
+
+  class M(torch.nn.Module):
+     def __init__(self):
+        super().__init__()
+        self.linear = torch.nn.Linear(1024, 1000)
+
+     def forward(self, x):
+        return self.linear(x)
+
+  example_inputs = (torch.randn(1, 1024),)
+  m = M()
+
+  # Step 1. program capture
+  # NOTE: this API will be updated to torch.export API in the future, but the captured
+  # result shoud mostly stay the same
+  exported_model = capture_pre_autograd_graph(m, example_inputs)
+  # we get a model with aten ops
+
+  # Step 2. quantization-aware training
+  # Use Backend Quantizer for X86 CPU
+  quantizer = X86InductorQuantizer()
+  quantizer.set_global(xiq.get_default_x86_inductor_quantization_config(is_qat=True))
+  prepared_model = prepare_qat_pt2e(exported_model, quantizer)
+
+  # train omitted
+
+  converted_model = convert_pt2e(prepared_model)
+  # we have a model with aten ops doing integer computations when possible
+
+  # move the quantized model to eval mode, equivalent to `m.eval()`
+  torch.ao.quantization.move_exported_model_to_eval(converted_model)
+
+  # Lower the model into Inductor
+  with torch.no_grad():
+    optimized_model = torch.compile(converted_model)
+    _ = optimized_model(*example_inputs)
+
+Please note that the Inductor ``freeze`` feature is not enabled by default.
+To use this feature, you need to run example code with ``TORCHINDUCTOR_FREEZING=1``.
+
+For example:
+
+::
+
+    TORCHINDUCTOR_FREEZING=1 python example_x86inductorquantizer_qat.py
+
+Conclusion
+------------
 
 With this tutorial, we introduce how to use Inductor with X86 CPU in PyTorch 2 Quantization. Users can learn about
 how to use ``X86InductorQuantizer`` to quantize a model and lower it into the inductor with X86 CPU devices.