Add README section for TPU and address comments.

Author: jysohn23

examples/README.md

@@ -6,6 +6,7 @@ similar API between the different models.
 | Section                    | Description                                                                                                                                                |
 |----------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | [TensorFlow 2.0 models on GLUE](#TensorFlow-2.0-Bert-models-on-GLUE) | Examples running BERT TensorFlow 2.0 model on the GLUE tasks. 
+| [Running on TPUs](#running-on-tpus) | Examples on running fine-tuning tasks on Google TPUs to accelerate workloads. |
 | [Language Model fine-tuning](#language-model-fine-tuning) | Fine-tuning the library models for language modeling on a text dataset. Causal language modeling for GPT/GPT-2, masked language modeling for BERT/RoBERTa. |
 | [Language Generation](#language-generation) | Conditional text generation using the auto-regressive models of the library: GPT, GPT-2, Transformer-XL and XLNet.                                         |
 | [GLUE](#glue) | Examples running BERT/XLM/XLNet/RoBERTa on the 9 GLUE tasks. Examples feature distributed training as well as half-precision.                              |
@@ -36,6 +37,48 @@ Quick benchmarks from the script (no other modifications):
 
 Mixed precision (AMP) reduces the training time considerably for the same hardware and hyper-parameters (same batch size was used).
 
+## Running on TPUs
+
+You can accelerate your workloads on Google's TPUs. For information on how to setup your TPU environment refer to this
+[README](https://github.com/pytorch/xla/blob/master/README.md).
+
+The following are some examples of running the `*_tpu.py` finetuning scripts on TPUs. All steps for data preparation are
+identical to your normal GPU + Huggingface setup.
+
+### GLUE
+
+Before running anyone of these GLUE tasks you should download the
+[GLUE data](https://gluebenchmark.com/tasks) by running
+[this script](https://gist.github.com/W4ngatang/60c2bdb54d156a41194446737ce03e2e)
+and unpack it to some directory `$GLUE_DIR`.
+
+For running your GLUE task on MNLI dataset you can run something like the following:
+
+```
+export GLUE_DIR=/path/to/glue
+export TASK_NAME=MNLI
+
+python run_glue_tpu.py \
+  --model_type bert \
+  --model_name_or_path bert-base-cased \
+  --task_name $TASK_NAME \
+  --do_train \
+  --do_eval \
+  --do_lower_case \
+  --data_dir $GLUE_DIR/$TASK_NAME \
+  --max_seq_length 128 \
+  --train_batch_size 32 \
+  --learning_rate 3e-5 \
+  --num_train_epochs 3.0 \
+  --output_dir /tmp/$TASK_NAME \
+  --overwrite_output_dir \
+  --logging_steps 50 \
+  --save_steps 200 \
+  --num_cores=8 \
+  --only_log_master
+```
+
+
 ## Language model fine-tuning
 
 Based on the script [`run_lm_finetuning.py`](https://github.com/huggingface/transformers/blob/master/examples/run_lm_finetuning.py).

examples/run_glue_tpu.py

@@ -1,5 +1,6 @@
 # coding=utf-8
 # Copyright 2019 The Google AI Language Team Authors and The HuggingFace Inc. team.
+# Copyright (c) 2019, NVIDIA CORPORATION.  All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -77,8 +78,8 @@ def set_seed(args):
 def get_sampler(dataset):
     if xm.xrt_world_size() <= 1:
         return RandomSampler(dataset)
-    return DistributedSampler(dataset,
-            num_replicas=xm.xrt_world_size(), rank=xm.get_ordinal())
+    return DistributedSampler(
+            dataset, num_replicas=xm.xrt_world_size(), rank=xm.get_ordinal())
 
 
 def train(args, train_dataset, model, tokenizer, disable_logging=False):
@@ -97,8 +98,14 @@ def train(args, train_dataset, model, tokenizer, disable_logging=False):
     # Prepare optimizer and schedule (linear warmup and decay)
     no_decay = ['bias', 'LayerNorm.weight']
     optimizer_grouped_parameters = [
-        {'params': [p for n, p in model.named_parameters() if not any(nd in n for nd in no_decay)], 'weight_decay': args.weight_decay},
-        {'params': [p for n, p in model.named_parameters() if any(nd in n for nd in no_decay)], 'weight_decay': 0.0},
+        {
+            'params': [p for n, p in model.named_parameters() if not any(nd in n for nd in no_decay)],
+            'weight_decay': args.weight_decay,
+        },
+        {
+            'params': [p for n, p in model.named_parameters() if any(nd in n for nd in no_decay)],
+            'weight_decay': 0.0,
+        },
     ]
     optimizer = AdamW(optimizer_grouped_parameters, lr=args.learning_rate, eps=args.adam_epsilon)
     scheduler = WarmupLinearSchedule(optimizer, warmup_steps=args.warmup_steps, t_total=t_total)
@@ -129,8 +136,7 @@ def train(args, train_dataset, model, tokenizer, disable_logging=False):
                 logger.info("Saving model checkpoint to %s", output_dir)
                 if not os.path.exists(output_dir):
                     os.makedirs(output_dir)
-                model_to_save = model.module if hasattr(model, 'module') else model  # Take care of distributed/parallel training
-                model_to_save.save_pretrained(output_dir, xla_device=True)
+                model.save_pretrained(output_dir, xla_device=True)
                 torch.save(args, os.path.join(output_dir, 'training_args.bin'))
 
             model.train()
@@ -144,6 +150,7 @@ def train(args, train_dataset, model, tokenizer, disable_logging=False):
             loss = outputs[0]  # model outputs are always tuple in transformers (see doc)
 
             if args.gradient_accumulation_steps > 1:
+                xm.mark_step()  # Mark step to evaluate graph so far or else graph will grow too big and OOM.
                 loss = loss / args.gradient_accumulation_steps
 
             loss.backward()
@@ -350,25 +357,24 @@ def main(args):
 
     logger.info("Training/evaluation parameters %s", args)
 
-    # Training
     if args.do_train:
+        # Train the model.
         train_dataset = load_and_cache_examples(args, args.task_name, tokenizer, evaluate=False)
         global_step, tr_loss = train(args, train_dataset, model, tokenizer, disable_logging=disable_logging)
         logger.info(" global_step = %s, average loss = %s", global_step, tr_loss)
 
+        # Save trained model.
+        # Saving best-practices: if you use defaults names for the model, you can reload it using from_pretrained()
+        output_dir = os.path.join(args.output_dir, 'final-xla{}'.format(xm.get_ordinal()))
 
-    # Saving best-practices: if you use defaults names for the model, you can reload it using from_pretrained()
-    output_dir = os.path.join(args.output_dir, 'final-xla{}'.format(xm.get_ordinal()))
-    if args.do_train:
         # Create output directory if needed
         if not os.path.exists(output_dir):
             os.makedirs(output_dir)
 
         logger.info("Saving model checkpoint to %s", output_dir)
         # Save a trained model, configuration and tokenizer using `save_pretrained()`.
         # They can then be reloaded using `from_pretrained()`
-        model_to_save = model.module if hasattr(model, 'module') else model  # Take care of distributed/parallel training
-        model_to_save.save_pretrained(output_dir, xla_device=True)
+        model.save_pretrained(output_dir, xla_device=True)
         tokenizer.save_pretrained(output_dir)
 
         # Good practice: save your training arguments together with the trained.