Add run_glue_tpu.py that trains models on TPUs (#3702)

* Initial commit to get BERT + run_glue.py on TPU

* Add README section for TPU and address comments.

* Cleanup TPU bits from run_glue.py (#3)

TPU runner is currently implemented in:
https://github.com/pytorch-tpu/transformers/blob/tpu/examples/run_glue_tpu.py.

We plan to upstream this directly into `huggingface/transformers`
(either `master` or `tpu`) branch once it's been more thoroughly tested.

* Cleanup TPU bits from run_glue.py

TPU runner is currently implemented in:
https://github.com/pytorch-tpu/transformers/blob/tpu/examples/run_glue_tpu.py.

We plan to upstream this directly into `huggingface/transformers`
(either `master` or `tpu`) branch once it's been more thoroughly tested.

* No need to call `xm.mark_step()` explicitly (#4)

Since for gradient accumulation we're accumulating on batches from
`ParallelLoader` instance which on next() marks the step itself.

* Resolve R/W conflicts from multiprocessing (#5)

* Add XLNet in list of models for `run_glue_tpu.py` (#6)

* Add RoBERTa to list of models in TPU GLUE (#7)

* Add RoBERTa and DistilBert to list of models in TPU GLUE (#8)

* Use barriers to reduce duplicate work/resources (#9)

* Shard eval dataset and aggregate eval metrics (#10)

* Shard eval dataset and aggregate eval metrics

Also, instead of calling `eval_loss.item()` every time do summation with
tensors on device.

* Change defaultdict to float

* Reduce the pred, label tensors instead of metrics

As brought up during review some metrics like f1 cannot be aggregated
via averaging. GLUE task metrics depends largely on the dataset, so
instead we sync the prediction and label tensors so that the metrics can
be computed accurately on those instead.

* Only use tb_writer from master (#11)

* Apply huggingface black code formatting

* Style

* Remove `--do_lower_case` as example uses cased

* Add option to specify tensorboard logdir

This is needed for our testing framework which checks regressions
against key metrics writtern by the summary writer.

* Using configuration for `xla_device`

* Prefix TPU specific comments.

* num_cores clarification and namespace eval metrics

* Cache features file under `args.cache_dir`

Instead of under `args.data_dir`. This is needed as our test infra uses
data_dir with a read-only filesystem.

* Rename `run_glue_tpu` to `run_tpu_glue`

Co-authored-by: LysandreJik <lysandre.debut@reseau.eseo.fr>

src/transformers/modeling_utils.py

@@ -323,6 +323,9 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin):
     def save_pretrained(self, save_directory):
         """ Save a model and its configuration file to a directory, so that it
             can be re-loaded using the `:func:`~transformers.PreTrainedModel.from_pretrained`` class method.
+
+            Arguments:
+                save_directory: directory to which to save.
         """
         assert os.path.isdir(
             save_directory
@@ -334,12 +337,21 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin):
         # Attach architecture to the config
         model_to_save.config.architectures = [model_to_save.__class__.__name__]
 
-        # Save configuration file
-        model_to_save.config.save_pretrained(save_directory)
-
         # If we save using the predefined names, we can load using `from_pretrained`
         output_model_file = os.path.join(save_directory, WEIGHTS_NAME)
-        torch.save(model_to_save.state_dict(), output_model_file)
+
+        if hasattr(self.config, "xla_device") and self.config.xla_device:
+            import torch_xla.core.xla_model as xm
+
+            if xm.is_master_ordinal():
+                # Save configuration file
+                model_to_save.config.save_pretrained(save_directory)
+            # xm.save takes care of saving only from master
+            xm.save(model_to_save.state_dict(), output_model_file)
+        else:
+            model_to_save.config.save_pretrained(save_directory)
+            torch.save(model_to_save.state_dict(), output_model_file)
+
         logger.info("Model weights saved in {}".format(output_model_file))
 
     @classmethod
@@ -626,6 +638,12 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin):
             }
             return model, loading_info
 
+        if hasattr(config, "xla_device") and config.xla_device:
+            import torch_xla.core.xla_model as xm
+
+            model = xm.send_cpu_data_to_device(model, xm.xla_device())
+            model = model.to(xm.xla_device())
+
         return model
 
     def prepare_inputs_for_generation(self, input_ids, **kwargs):