update readme - fix SQuAD model on multi-GPU

Author: thomwolf

README.md

@@ -194,3 +194,8 @@ python run_squad.py \
   --doc_stride 128 \
   --output_dir ../debug_squad/
 ```
+
+Training with the previous hyper-parameters and a batch size 32 (on 4 GPUs) for 2 epochs gave us the following results:
+```bash
+{"f1": 88.19829549714827, "exact_match": 80.75685903500474}
+```

modeling.py

@@ -455,9 +455,11 @@ def forward(self, input_ids, token_type_ids, attention_mask, start_positions=Non
         end_logits = end_logits.squeeze(-1)
 
         if start_positions is not None and end_positions is not None:
-            # If we are on multi-GPU, split add a dimension - if not this is a no-op
-            start_positions = start_positions.squeeze(-1)
-            end_positions = end_positions.squeeze(-1)
+            # If we are on multi-GPU, split add a dimension
+            if len(start_positions.size()) > 1:
+                start_positions = start_positions.squeeze(-1)
+            if len(end_positions.size()) > 1:
+                end_positions = end_positions.squeeze(-1)
             # sometimes the start/end positions are outside our model inputs, we ignore these terms
             ignored_index = start_logits.size(1)
             start_positions.clamp_(0, ignored_index)