Add predict step accumulation (#7767)

* Add eval_accumulation_step and clean distributed eval

* Add TPU test

* Add TPU stuff

* Fix arg name

* Fix Seq2SeqTrainer

* Fix total_size

* Update src/transformers/trainer_pt_utils.py

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Doc and add test to TPU

* Add unit test

* Adapt name

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

tests/test_trainer_tpu.py

@@ -0,0 +1,119 @@
+# This test is meant to be run in on an instance with TPUs like this:
+#
+#   python examples/xla_spawn.py --num_cores=8 tests/test_trainer_tpu.py
+#
+# Replace 8 with the number of TPU cores you have.
+#
+
+import sys
+from typing import Dict
+
+from transformers import EvalPrediction, HfArgumentParser, TrainingArguments, is_torch_available
+from transformers.utils import logging
+
+
+logger = logging.get_logger(__name__)
+
+
+if is_torch_available():
+    import torch
+    from torch import nn
+    from torch.utils.data.dataset import Dataset
+
+    from transformers import Trainer
+
+    class DummyDataset(Dataset):
+        def __init__(self, length: int = 101):
+            self.length = length
+
+        def __len__(self):
+            return self.length
+
+        def __getitem__(self, i) -> int:
+            return i
+
+    class DummyDataCollator:
+        def __call__(self, features):
+            return {"input_ids": torch.tensor(features), "labels": torch.tensor(features)}
+
+    class DummyModel(nn.Module):
+        def __init__(self):
+            super().__init__()
+            # Add some (unused) params otherwise DDP will complain.
+            self.fc = nn.Linear(120, 80)
+
+        def forward(self, input_ids, labels=None):
+            if labels is not None:
+                return torch.tensor(0.0, device=input_ids.device), input_ids
+            else:
+                return input_ids
+
+
+def main():
+    parser = HfArgumentParser((TrainingArguments,))
+    sys.argv += ["--output_dir", "./examples"]
+    training_args = parser.parse_args_into_dataclasses()[0]
+
+    logger.warning(
+        "Process rank: %s, device: %s, tpu_num_cores: %s",
+        training_args.local_rank,
+        training_args.device,
+        training_args.tpu_num_cores,
+    )
+
+    # Essentially, what we want to verify in the distributed case is
+    # that we get all samples back, in the right order.
+    # (this is crucial for prediction for instance)
+    for dataset_length in [1001, 256, 15]:
+        dataset = DummyDataset(dataset_length)
+
+        def compute_metrics(p: EvalPrediction) -> Dict:
+            sequential = list(range(len(dataset)))
+            success = p.predictions.tolist() == sequential and p.label_ids.tolist() == sequential
+            return {"success": success}
+
+        trainer = Trainer(
+            model=DummyModel(),
+            args=training_args,
+            data_collator=DummyDataCollator(),
+            eval_dataset=dataset,
+            compute_metrics=compute_metrics,
+        )
+        metrics = trainer.evaluate()
+        logger.info(metrics)
+        if metrics["eval_success"] is not True:
+            logger.error(metrics)
+            exit(1)
+
+        p = trainer.predict(dataset)
+        logger.info(p.metrics)
+        if p.metrics["eval_success"] is not True:
+            logger.error(p.metrics)
+            exit(1)
+
+        trainer.args.eval_accumulation_steps = 2
+
+        metrics = trainer.evaluate()
+        logger.info(metrics)
+        if metrics["eval_success"] is not True:
+            logger.error(metrics)
+            exit(1)
+
+        p = trainer.predict(dataset)
+        logger.info(p.metrics)
+        if p.metrics["eval_success"] is not True:
+            logger.error(p.metrics)
+            exit(1)
+
+        trainer.args.eval_accumulation_steps = None
+
+    logger.info("🔥 All distributed tests successful")
+
+
+def _mp_fn(index):
+    # For xla_spawn (TPUs)
+    main()
+
+
+if __name__ == "__main__":
+    main()