Refine the LLM manual (focus on the debugging and profiling part) (#2952)

Summary:
Pull Request resolved: #2952

* Some auto-formatting by my VSCode (remove extra spaces)
* Remove imports that have been imported in previous part of the doc
* Other minor changes to keep consistency across the doc
* Link a screenshot instead of using the raw table because the original table is illegible:
 {F1482781056}

Differential Revision: D55938344

Author: Olivia-liu

docs/source/_static/img/llm_manual_print_data_tabular.png

@@ -14,7 +14,7 @@
 
 ## Prerequisites
 
-To follow this guide, you'll need to clone the ExecuTorch repository and install dependencies. 
+To follow this guide, you'll need to clone the ExecuTorch repository and install dependencies.
 ExecuTorch recommends Python 3.10 and the use of Conda to manage your environment. Conda is not
 required, though be aware that you may need to replace the use of python/pip with python3/pip3
 depending on your environment.
@@ -82,7 +82,7 @@ For more information, see [Setting Up ExecuTorch](https://pytorch.org/executorch
 
 ## Running a Large Language Model Locally
 
-This example uses Karpathy’s [NanoGPT](https://github.com/karpathy/nanoGPT), which is a minimal implementation of 
+This example uses Karpathy’s [NanoGPT](https://github.com/karpathy/nanoGPT), which is a minimal implementation of
 GPT-2 124M. This guide is applicable to other language models, as ExecuTorch is model-invariant.
 
 There are two steps to running a model with ExecuTorch:
@@ -129,7 +129,7 @@ Create a file called export_nanogpt.py with the following contents:
 
 import torch
 
-from executorch.exir import EdgeCompileConfig,  to_edge
+from executorch.exir import EdgeCompileConfig, to_edge
 from torch.nn.attention import sdpa_kernel, SDPBackend
 from torch._export import capture_pre_autograd_graph
 from torch.export import export
@@ -139,7 +139,7 @@ from model import GPT
 # Load the model.
 model = GPT.from_pretrained('gpt2')
 
-# Create example inputs. This is used in the export process to provide 
+# Create example inputs. This is used in the export process to provide
 # hints on the expected shape of the model input.
 example_inputs = (torch.randint(0, 100, (1, 8), dtype=torch.long), )
 
@@ -211,8 +211,8 @@ std::string generate(
     BasicSampler& sampler,
     size_t max_output_length) {
 
-    // Convert the input text into a list of integers (tokens) that represents 
-    // it, using the string-to-token mapping that the model was trained on. 
+    // Convert the input text into a list of integers (tokens) that represents
+    // it, using the string-to-token mapping that the model was trained on.
     // Each token is an integer that represents a word or part of a word.
     std::vector<int64_t> input_tokens = tokenizer.encode(prompt);
     std::vector<int64_t> output_tokens;
@@ -221,8 +221,8 @@ std::string generate(
         // Convert the input_tokens from a vector of int64_t to EValue.
         // EValue is a unified data type in the ExecuTorch runtime.
         ManagedTensor tensor_tokens(
-            input_tokens.data(), 
-            {1, static_cast<int>(input_tokens.size())}, 
+            input_tokens.data(),
+            {1, static_cast<int>(input_tokens.size())},
             ScalarType::Long);
         std::vector<EValue> inputs = {tensor_tokens.get_tensor()};
 
@@ -232,7 +232,7 @@ std::string generate(
         // Convert the output logits from EValue to std::vector, which is what
         // the sampler expects.
         Tensor logits_tensor = logits_evalue.get()[0].toTensor();
-        std::vector<float> logits(logits_tensor.data_ptr<float>(), 
+        std::vector<float> logits(logits_tensor.data_ptr<float>(),
             logits_tensor.data_ptr<float>() + logits_tensor.numel());
 
         // Sample the next token from the logits.
@@ -255,9 +255,9 @@ std::string generate(
 }
 ```
 
-The `Module` class handles loading the .pte file and preparing for execution. 
+The `Module` class handles loading the .pte file and preparing for execution.
 
-The tokenizer is responsible for converting from a human-readable string representation of the prompt to the 
+The tokenizer is responsible for converting from a human-readable string representation of the prompt to the
 numerical form expected by the model. To do this, the tokenzier associates short substrings with a given token ID.
 The tokens can be thought of as representing words or parts of words, though, in-practice, they may be arbitrary
 sequences of characters.
@@ -312,7 +312,7 @@ and the [ExecuTorch Runtime API Reference](https://pytorch.org/executorch/main/e
 
 ExecuTorch uses the CMake build system. To compile and link against the ExecuTorch runtime,
 include the ExecuTorch project via `add_directory` and link against `executorch` and additional
-dependencies. 
+dependencies.
 
 Create a file named CMakeLists.txt with the following content:
 
@@ -374,7 +374,7 @@ specific hardware (delegation), and because it is doing all of the calculations
 
 ## Delegation
 
-While ExecuTorch provides a portable, cross-platform implementation for all operators, it also provides specialized 
+While ExecuTorch provides a portable, cross-platform implementation for all operators, it also provides specialized
 backends for a number of different targets. These include, but are not limited to, x86 and ARM CPU acceleration via
 the XNNPACK backend, Apple acceleration via the CoreML backend and Metal Performance Shader (MPS) backend, and GPU
 acceleration via the Vulkan backend.
@@ -395,11 +395,10 @@ To delegate to the XNNPACK backend, call `to_backend` with an instance of `Xnnpa
 
 from executorch.backends.xnnpack.partition.xnnpack_partitioner import XnnpackPartitioner
 from executorch.backends.xnnpack.utils.configs import get_xnnpack_edge_compile_config
-from executorch.exir import EdgeCompileConfig, to_edge
 
 #...
 
-edge_config = edge_config = get_xnnpack_edge_compile_config()
+edge_config = get_xnnpack_edge_compile_config()
 edge_manager = to_edge(traced_model, compile_config=edge_config)
 
 # Delegate to the XNNPACK backend.
@@ -433,15 +432,15 @@ and [CoreML Backend](https://pytorch.org/executorch/stable/build-run-coreml.html
 ## Quantization
 
 Quantization refers to a set of techniques for running calculations and storing tensors using lower precision types.
-Compared to 32-bit floating point, using 8-bit integers can provide both a significant speedup and reduction in 
-memory usage. There are many approaches to quantizing a model, varying in amount of pre-processing required, data 
+Compared to 32-bit floating point, using 8-bit integers can provide both a significant speedup and reduction in
+memory usage. There are many approaches to quantizing a model, varying in amount of pre-processing required, data
 types used, and impact on model accuracy and performance.
 
 Because compute and memory are highly constrained on mobile devices, some form of quantization is necessary to ship
 large models on consumer electronics. In particular, large language models, such as Llama2, may require quantizing
 model weights to 4 bits or less.
 
-Leveraging quantization requires transforming the model before export. PyTorch provides the pt2e (PyTorch 2 Export) 
+Leveraging quantization requires transforming the model before export. PyTorch provides the pt2e (PyTorch 2 Export)
 API for this purpose. This example targets CPU acceleration using the XNNPACK delegate. As such, it needs to use the
  XNNPACK-specific quantizer. Targeting a different backend will require use of the corresponding quantizer.
 
@@ -504,14 +503,14 @@ et_program = edge_manager.to_executorch()
 Finally, ensure that the runner links against the `xnnpack_backend` target in CMakeLists.txt.
 
 ```
-add_executable(nanogpt_runner nanogpt_runner.cpp)
+add_executable(nanogpt_runner main.cpp)
 target_link_libraries(
     nanogpt_runner
     PRIVATE
-    etdump
-    extension_module
-    portable_ops_lib
-    xnnpack_backend) # Link the XNNPACK backend
+    executorch
+    extension_module_static # Provides the Module class
+    optimized_native_cpu_ops_lib # Provides baseline cross-platform kernels
+    xnnpack_backend) # Provides the XNNPACK CPU acceleration backend
 ```
 
 For more information, see [Quantization in ExecuTorch](https://pytorch.org/executorch/stable/quantization-overview.html).
@@ -530,6 +529,7 @@ The `get_delegation_info()` method provides a summary of what happened to the mo
 from executorch.exir.backend.utils import get_delegation_info
 from tabulate import tabulate
 
+# ... After call to to_backend(), but before to_executorch()
 graph_module = edge_manager.exported_program().graph_module
 delegation_info = get_delegation_info(graph_module)
 print(delegation_info.get_summary())
@@ -564,7 +564,7 @@ from executorch.exir.backend.utils import print_delegated_graph
 graph_module = edge_manager.exported_program().graph_module
 print(print_delegated_graph(graph_module))
 ```
-This may generate a large amount of output for large models. Consider using "Control+F" or "Command+F" to locate the operator you’re interested in 
+This may generate a large amount of output for large models. Consider using "Control+F" or "Command+F" to locate the operator you’re interested in
 (e.g. “aten_view_copy_default”). Observe which instances are not under lowered graphs.
 
 In the fragment of the output for NanoGPT below, observe that embedding and add operators are delegated to XNNPACK while the sub operator is not.
@@ -600,12 +600,12 @@ In your export script, after calling `to_edge()` and `to_executorch()`, call `ge
 import copy
 
 # Make the deep copy immediately after to to_edge()
-edge_program_manager_copy = copy.deepcopy(edge_program_manager)
+edge_manager_copy = copy.deepcopy(edge_manager)
 
 # ...
 # Generate ETRecord right after to_executorch()
 etrecord_path = "etrecord.bin"
-generate_etrecord(etrecord_path, edge_program_manager_copy, et_program_manager)
+generate_etrecord(etrecord_path, edge_manager_copy, et_program)
 ```
 
 Run the export script and the ETRecord will be generated as `etrecord.bin`.
@@ -624,13 +624,14 @@ Include the ETDump header in your code.
 Create an Instance of the ETDumpGen class and pass it to the Module constructor.
 ```cpp
 std::unique_ptr<torch::executor::ETDumpGen> etdump_gen_ = std::make_unique<torch::executor::ETDumpGen>();
-Module llm_model("nanogpt.pte", Module::MlockConfig::UseMlock, std::move(etdump_gen_));
+Module model("nanogpt.pte", torch::executor::Module::MlockConfig::UseMlockIgnoreErrors, std::move(etdump_gen_));
 ```
 
-After execution, save the ETDump to a file. You can capture multiple model runs in a single trace, if desired.
+After calling `generate()`, save the ETDump to a file. You can capture multiple
+model runs in a single trace, if desired.
 ```cpp
 torch::executor::ETDumpGen* etdump_gen =
-    static_cast<torch::executor::ETDumpGen*>(llm_model.event_tracer());
+    static_cast<torch::executor::ETDumpGen*>(model.event_tracer());
 
 ET_LOG(Info, "ETDump size: %zu blocks", etdump_gen->get_num_blocks());
 etdump_result result = etdump_gen->get_etdump_data();
@@ -643,9 +644,22 @@ if (result.buf != nullptr && result.size > 0) {
 }
 ```
 
-Compile the ExecuTorch runtime with the `ET_EVENT_TRACER_ENABLED` pre-processor flag to enable events to be traced and logged into ETDump inside the ExecuTorch runtime. Add these to your CMakeLists.txt
+Additionally, update CMakeLists.txt to build with SDK and enable events to be traced and logged into ETDump:
 
 ```
+option(EXECUTORCH_BUILD_SDK "" ON)
+
+# ...
+
+target_link_libraries(
+    nanogpt_runner
+    PRIVATE
+    executorch
+    extension_module_static # Provides the Module class
+    optimized_native_cpu_ops_lib # Provides baseline cross-platform kernels
+    xnnpack_backend # Provides the XNNPACK CPU acceleration backend
+    etdump) # Provides event tracing and logging
+
 target_compile_options(executorch PUBLIC -DET_EVENT_TRACER_ENABLED)
 target_compile_options(portable_ops_lib PUBLIC -DET_EVENT_TRACER_ENABLED)
 ```
@@ -658,20 +672,15 @@ Once you’ve collected debug artifacts ETDump (and optionally an ETRecord), you
 ```python
 from executorch.sdk import Inspector
 
-inspector = Inspector(etdump_path="etdump.etdp", etrecord="etrecord.bin")
-# If you did not generate an ETRecord, then just pass in the ETDump: `inspector = Inspector(etdump_path="etdump.etdp")`
+inspector = Inspector(etdump_path="etdump.etdp")
+# If you also generated an ETRecord, then pass that in as well: `inspector = Inspector(etdump_path="etdump.etdp", etrecord="etrecord.bin")`
 
-inspector.print_data_tabular()
+with open("inspector_out.txt", "w") as file:
+    inspector.print_data_tabular(file)
 ```
 This prints the performance data in a tabular format in “inspector_out.txt”, with each row being a profiling event.
-
-|  |  event_block_name  |  event_name  |  p10  (ms)  |  p50  (ms)  |  p90  (ms)  |  avg  (ms)  |  min  (ms)  |  max  (ms)  |  op_types  |  is_delegated_op  |  delegate_backend_name  |
-|---|----------------------|------------------|-----------|---------------|--------------|-------------|-------------|--------------|-------------|---------------------------|----------|
-|  0  |  Default  |  Method::init  |  60.502  |  60.502  |  60.502  |  60.502  |  60.502  |  60.502  |  []  |  False  |  |
-|  1  |  Default  |  Program::load_method  |  60.5114  |  60.5114  |  60.5114  |  60.5114  |  60.5114  |  60.5114  |  []  |  False  |  |
-|  2  |  Execute  |  native_call_arange.start_out  |  0.029583  |  0.029583  |  0.029583  |  0.029583  |  0.029583  |  0.029583  |  []  |  False  |  |
-|  3  |  Execute  |  native_call_embedding.out  |  0.022916  |  0.022916  |  0.022916  |  0.022916  |  0.022916  |  0.022916  |  []  |  False  |  |
-|  4  |  Execute  |  native_call_embedding.out  |  0.001084  |  0.001084  |  0.001084  |  0.001084  |  0.001084  |  0.001084  |  []  |  False  |  |
+![](../_static/img/llm_manual_print_data_tabular.png)
+<a href="../_static/img/llm_manual_print_data_tabular.png" target="_blank">View in full size</a>
 
 To learn more about the Inspector and the rich functionality it provides, see the [Inspector API Reference](https://pytorch.org/executorch/main/sdk-inspector.html).