[fx/profiler] debug the fx.profiler / add an example test script for fx.profiler (#1730)

* [fx/profiler] add test.

* [fx] fix file names.

* [fx] add docstring and comment.

* [fx] polish profiler.py.

* [fx] fix import errors.

* [fx] fix profiler.

* [fx] fix names.

tests/test_fx/test_profiler/gpt_utils.py

@@ -0,0 +1,50 @@
+import torch
+import torch.nn as nn
+from transformers import GPT2Config, GPT2LMHeadModel
+
+
+class GPTLMModel(nn.Module):
+
+    def __init__(self,
+                 hidden_size=768,
+                 num_layers=12,
+                 num_attention_heads=12,
+                 max_seq_len=1024,
+                 vocab_size=50257,
+                 checkpoint=False):
+        super().__init__()
+        self.checkpoint = checkpoint
+        self.model = GPT2LMHeadModel(
+            GPT2Config(n_embd=hidden_size,
+                       n_layer=num_layers,
+                       n_head=num_attention_heads,
+                       n_positions=max_seq_len,
+                       n_ctx=max_seq_len,
+                       vocab_size=vocab_size))
+        if checkpoint:
+            self.model.gradient_checkpointing_enable()
+
+    def forward(self, input_ids, attention_mask):
+        # Only return lm_logits
+        return self.model(input_ids=input_ids, attention_mask=attention_mask, use_cache=not self.checkpoint)[0]
+
+
+class GPTLMLoss(nn.Module):
+
+    def __init__(self):
+        super().__init__()
+        self.loss_fn = nn.CrossEntropyLoss()
+
+    def forward(self, logits, labels):
+        shift_logits = logits[..., :-1, :].contiguous()
+        shift_labels = labels[..., 1:].contiguous()
+        # Flatten the tokens
+        return self.loss_fn(shift_logits.view(-1, shift_logits.size(-1)), shift_labels.view(-1))
+
+
+def gpt2_medium(checkpoint=False):
+    return GPTLMModel(hidden_size=1024, num_layers=24, num_attention_heads=16, checkpoint=checkpoint)
+
+
+def gpt2_xl(checkpoint=False):
+    return GPTLMModel(hidden_size=1600, num_layers=48, num_attention_heads=32, checkpoint=checkpoint)