Tpu trainer (#4146)

* wip

* wip

* a last wip

* Better logging when using TPUs

* Correct argument name

* Tests

* fix

* Metrics in evaluation

* Update src/transformers/training_args.py

* [tpu] Use launcher script instead

* [tpu] lots of tweaks

* Fix formatting
Co-authored-by: Julien Chaumond <chaumond@gmail.com>

examples/run_glue.py

@@ -202,5 +202,10 @@ def main():
     return results
 
 
+def _mp_fn(index):
+    # For xla_spawn (TPUs)
+    main()
+
+
 if __name__ == "__main__":
     main()

examples/xla_spawn.py

+"""
+A simple launcher script for TPU training
+
+Inspired by https://github.com/pytorch/pytorch/blob/master/torch/distributed/launch.py
+
+::
+    >>> python xla_spawn.py --num_cores=NUM_CORES_YOU_HAVE
+               YOUR_TRAINING_SCRIPT.py (--arg1 --arg2 --arg3 and all other
+               arguments of your training script)
+
+"""
+
+
+import importlib
+import os
+import sys
+from argparse import REMAINDER, ArgumentParser
+
+import torch_xla.distributed.xla_multiprocessing as xmp
+
+
+def trim_suffix(s: str, suffix: str):
+    return s if not s.endswith(suffix) or len(suffix) == 0 else s[: -len(suffix)]
+
+
+def parse_args():
+    """
+    Helper function parsing the command line options
+    @retval ArgumentParser
+    """
+    parser = ArgumentParser(
+        description=(
+            "PyTorch TPU distributed training launch "
+            "helper utility that will spawn up "
+            "multiple distributed processes"
+        )
+    )
+
+    # Optional arguments for the launch helper
+    parser.add_argument("--num_cores", type=int, default=1, help="Number of TPU cores to use (1 or 8).")
+
+    # positional
+    parser.add_argument(
+        "training_script",
+        type=str,
+        help=(
+            "The full module name to the single TPU training "
+            "program/script to be launched in parallel, "
+            "followed by all the arguments for the "
+            "training script"
+        ),
+    )
+
+    # rest from the training program
+    parser.add_argument("training_script_args", nargs=REMAINDER)
+
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
+
+    # Import training_script as a module.
+    mod_name = trim_suffix(os.path.basename(args.training_script), ".py")
+    mod = importlib.import_module(mod_name)
+
+    # Patch sys.argv
+    sys.argv = [args.training_script] + args.training_script_args + ["--tpu_num_cores", str(args.num_cores)]
+
+    xmp.spawn(mod._mp_fn, args=(), nprocs=args.num_cores)
+
+
+if __name__ == "__main__":
+    main()

src/transformers/trainer.py

@@ -21,7 +21,7 @@ from .data.data_collator import DataCollator, DefaultDataCollator
 from .modeling_utils import PreTrainedModel
 from .optimization import AdamW, get_linear_schedule_with_warmup
 from .trainer_utils import PREFIX_CHECKPOINT_DIR, EvalPrediction, PredictionOutput, TrainOutput
-from .training_args import TrainingArguments
+from .training_args import TrainingArguments, is_tpu_available
 
 
 try:
@@ -36,6 +36,11 @@ def is_apex_available():
     return _has_apex
 
 
+if is_tpu_available():
+    import torch_xla.core.xla_model as xm
+    import torch_xla.debug.metrics as met
+    import torch_xla.distributed.parallel_loader as pl
+
 try:
     from torch.utils.tensorboard import SummaryWriter
 
@@ -88,6 +93,12 @@ def torch_distributed_zero_first(local_rank: int):
         torch.distributed.barrier()
 
 
+def get_tpu_sampler(dataset: Dataset):
+    if xm.xrt_world_size() <= 1:
+        return RandomSampler(dataset)
+    return DistributedSampler(dataset, num_replicas=xm.xrt_world_size(), rank=xm.get_ordinal())
+
+
 class Trainer:
     """
     Trainer is a simple but feature-complete training and eval loop for PyTorch,
@@ -146,41 +157,73 @@ class Trainer:
             )
         set_seed(self.args.seed)
         # Create output directory if needed
-        if self.args.local_rank in [-1, 0]:
+        if self.is_local_master():
             os.makedirs(self.args.output_dir, exist_ok=True)
+        if is_tpu_available():
+            # Set an xla_device flag on the model's config.
+            # We'll find a more elegant and not need to do this in the future.
+            self.model.config.xla_device = True
 
     def get_train_dataloader(self) -> DataLoader:
         if self.train_dataset is None:
             raise ValueError("Trainer: training requires a train_dataset.")
-        train_sampler = (
-            RandomSampler(self.train_dataset) if self.args.local_rank == -1 else DistributedSampler(self.train_dataset)
-        )
-        return DataLoader(
+        if is_tpu_available():
+            train_sampler = get_tpu_sampler(self.train_dataset)
+        else:
+            train_sampler = (
+                RandomSampler(self.train_dataset)
+                if self.args.local_rank == -1
+                else DistributedSampler(self.train_dataset)
+            )
+
+        data_loader = DataLoader(
             self.train_dataset,
             batch_size=self.args.train_batch_size,
             sampler=train_sampler,
             collate_fn=self.data_collator.collate_batch,
         )
 
+        if is_tpu_available():
+            data_loader = pl.ParallelLoader(data_loader, [self.args.device]).per_device_loader(self.args.device)
+
+        return data_loader
+
     def get_eval_dataloader(self, eval_dataset: Optional[Dataset] = None) -> DataLoader:
         if eval_dataset is None and self.eval_dataset is None:
             raise ValueError("Trainer: evaluation requires an eval_dataset.")
-        return DataLoader(
+
+        sampler = get_tpu_sampler(eval_dataset) if is_tpu_available() else None
+
+        data_loader = DataLoader(
             eval_dataset if eval_dataset is not None else self.eval_dataset,
+            sampler=sampler,
             batch_size=self.args.eval_batch_size,
             shuffle=False,
             collate_fn=self.data_collator.collate_batch,
         )
 
+        if is_tpu_available():
+            data_loader = pl.ParallelLoader(data_loader, [self.args.device]).per_device_loader(self.args.device)
+
+        return data_loader
+
     def get_test_dataloader(self, test_dataset: Dataset) -> DataLoader:
         # We use the same batch_size as for eval.
-        return DataLoader(
+        sampler = get_tpu_sampler(test_dataset) if is_tpu_available() else None
+
+        data_loader = DataLoader(
             test_dataset,
+            sampler=sampler,
             batch_size=self.args.eval_batch_size,
             shuffle=False,
             collate_fn=self.data_collator.collate_batch,
         )
 
+        if is_tpu_available():
+            data_loader = pl.ParallelLoader(data_loader, [self.args.device]).per_device_loader(self.args.device)
+
+        return data_loader
+
     def get_optimizers(
         self, num_training_steps: int
     ) -> Tuple[torch.optim.Optimizer, torch.optim.lr_scheduler.LambdaLR]:
@@ -222,7 +265,6 @@ class Trainer:
                 If present, we will try reloading the optimizer/scheduler states from there.
         """
         train_dataloader = self.get_train_dataloader()
-
         if self.args.max_steps > 0:
             t_total = self.args.max_steps
             num_train_epochs = (
@@ -271,16 +313,21 @@ class Trainer:
             self._setup_wandb()
 
         # Train!
+        if is_tpu_available():
+            num_examples = len(train_dataloader._loader._loader.dataset)
+            total_train_batch_size = self.args.train_batch_size * xm.xrt_world_size()
+        else:
+            num_examples = len(train_dataloader.dataset)
+            total_train_batch_size = (
+                self.args.train_batch_size
+                * self.args.gradient_accumulation_steps
+                * (torch.distributed.get_world_size() if self.args.local_rank != -1 else 1),
+            )
         logger.info("***** Running training *****")
-        logger.info("  Num examples = %d", len(train_dataloader.dataset))
+        logger.info("  Num examples = %d", num_examples)
         logger.info("  Num Epochs = %d", num_train_epochs)
-        logger.info("  Instantaneous batch size per GPU = %d", self.args.per_gpu_train_batch_size)
-        logger.info(
-            "  Total train batch size (w. parallel, distributed & accumulation) = %d",
-            self.args.train_batch_size
-            * self.args.gradient_accumulation_steps
-            * (torch.distributed.get_world_size() if self.args.local_rank != -1 else 1),
-        )
+        logger.info("  Instantaneous batch size per device = %d", self.args.per_gpu_train_batch_size)
+        logger.info("  Total train batch size (w. parallel, distributed & accumulation) = %d", total_train_batch_size)
         logger.info("  Gradient Accumulation steps = %d", self.args.gradient_accumulation_steps)
         logger.info("  Total optimization steps = %d", t_total)
 
@@ -309,10 +356,10 @@ class Trainer:
         logging_loss = 0.0
         model.zero_grad()
         train_iterator = trange(
-            epochs_trained, int(num_train_epochs), desc="Epoch", disable=self.args.local_rank not in [-1, 0],
+            epochs_trained, int(num_train_epochs), desc="Epoch", disable=not self.is_local_master()
         )
         for epoch in train_iterator:
-            epoch_iterator = tqdm(train_dataloader, desc="Iteration", disable=self.args.local_rank not in [-1, 0])
+            epoch_iterator = tqdm(train_dataloader, desc="Iteration", disable=not self.is_local_master())
             for step, inputs in enumerate(epoch_iterator):
 
                 # Skip past any already trained steps if resuming training
@@ -332,12 +379,16 @@ class Trainer:
                     else:
                         torch.nn.utils.clip_grad_norm_(model.parameters(), self.args.max_grad_norm)
 
-                    optimizer.step()
+                    if is_tpu_available():
+                        xm.optimizer_step(optimizer)
+                    else:
+                        optimizer.step()
+
                     scheduler.step()
                     model.zero_grad()
                     global_step += 1
 
-                    if self.args.local_rank in [-1, 0]:
+                    if self.is_local_master():
                         if (self.args.logging_steps > 0 and global_step % self.args.logging_steps == 0) or (
                             global_step == 1 and self.args.logging_first_step
                         ):
@@ -371,6 +422,7 @@ class Trainer:
                                 assert model is self.model
                             # Save model checkpoint
                             output_dir = os.path.join(self.args.output_dir, f"{PREFIX_CHECKPOINT_DIR}-{global_step}")
+
                             self.save_model(output_dir)
                             self._rotate_checkpoints()
                             torch.save(optimizer.state_dict(), os.path.join(output_dir, "optimizer.pt"))
@@ -383,6 +435,9 @@ class Trainer:
             if self.args.max_steps > 0 and global_step > self.args.max_steps:
                 train_iterator.close()
                 break
+            if self.args.tpu_metrics_debug:
+                # tpu-comment: Logging debug metrics for PyTorch/XLA (compile, execute times, ops, etc.)
+                xm.master_print(met.metrics_report())
 
         if self.tb_writer:
             self.tb_writer.close()
@@ -413,12 +468,21 @@ class Trainer:
 
         return loss.item()
 
+    def is_local_master(self) -> bool:
+        if is_tpu_available():
+            return xm.is_master_ordinal(local=True)
+        else:
+            return self.args.local_rank in [-1, 0]
+
     def is_world_master(self) -> bool:
         """
         This will be True only in one process, even in distributed mode,
         even when training on multiple machines.
         """
-        return self.args.local_rank == -1 or torch.distributed.get_rank() == 0
+        if is_tpu_available():
+            return xm.is_master_ordinal(local=False)
+        else:
+            return self.args.local_rank == -1 or torch.distributed.get_rank() == 0
 
     def save_model(self, output_dir: Optional[str] = None):
         """
@@ -495,6 +559,11 @@ class Trainer:
         eval_dataloader = self.get_eval_dataloader(eval_dataset)
 
         output = self._prediction_loop(eval_dataloader, description="Evaluation")
+
+        if self.args.tpu_metrics_debug:
+            # tpu-comment: Logging debug metrics for PyTorch/XLA (compile, execute times, ops, etc.)
+            xm.master_print(met.metrics_report())
+
         return output.metrics
 
     def predict(self, test_dataset: Dataset) -> PredictionOutput:
@@ -558,6 +627,11 @@ class Trainer:
                     else:
                         label_ids = np.append(label_ids, inputs["labels"].detach().cpu().numpy(), axis=0)
 
+        if is_tpu_available():
+            # tpu-comment: Get all predictions and labels from all worker shards of eval dataset
+            preds = xm.mesh_reduce("eval_preds", preds, np.concatenate)
+            label_ids = xm.mesh_reduce("eval_out_label_ids", label_ids, np.concatenate)
+
         if self.compute_metrics is not None and preds is not None and label_ids is not None:
             metrics = self.compute_metrics(EvalPrediction(predictions=preds, label_ids=label_ids))
         else:

src/transformers/training_args.py

@@ -11,6 +11,19 @@ if is_torch_available():
     import torch
 
 
+try:
+    import torch_xla.core.xla_model as xm
+
+    _has_tpu = True
+except ImportError:
+    _has_tpu = False
+
+
+@torch_required
+def is_tpu_available():
+    return _has_tpu
+
+
 logger = logging.getLogger(__name__)
 
 
@@ -77,7 +90,7 @@ class TrainingArguments:
             )
         },
     )
-    no_cuda: bool = field(default=False, metadata={"help": "Avoid using CUDA even if it is available"})
+    no_cuda: bool = field(default=False, metadata={"help": "Do not use CUDA even when it is available"})
     seed: int = field(default=42, metadata={"help": "random seed for initialization"})
 
     fp16: bool = field(
@@ -95,6 +108,11 @@ class TrainingArguments:
     )
     local_rank: int = field(default=-1, metadata={"help": "For distributed training: local_rank"})
 
+    tpu_num_cores: Optional[int] = field(
+        default=None, metadata={"help": "TPU: Number of TPU cores (automatically passed by launcher script)"}
+    )
+    tpu_metrics_debug: bool = field(default=False, metadata={"help": "TPU: Whether to print debug metrics"})
+
     @property
     def train_batch_size(self) -> int:
         return self.per_gpu_train_batch_size * max(1, self.n_gpu)
@@ -110,6 +128,9 @@ class TrainingArguments:
         if self.no_cuda:
             device = torch.device("cpu")
             n_gpu = 0
+        elif is_tpu_available():
+            device = xm.xla_device()
+            n_gpu = 0
         elif self.local_rank == -1:
             # if n_gpu is > 1 we'll use nn.DataParallel.
             # If you only want to use a specific subset of GPUs use `CUDA_VISIBLE_DEVICES=0`