Sas gpu additions (#2308)

* Add batch_size and use_gpu to SAS from #2306

* Add batch_size and use_gpu to SAS from #2306

* Added docstrings for SAS-GPU to evluator.py

* Added docstrings for SAS-GPU to pipelines/base.py

* Typo fix in pipelines/base.py

* streamline docstrings with related params in code base

Co-authored-by: Thomas Stadelmann <thomas.stadelmann@deepset.ai>

haystack/nodes/evaluator/evaluator.py

@@ -393,6 +393,8 @@ def semantic_answer_similarity(
     predictions: List[List[str]],
     gold_labels: List[List[str]],
     sas_model_name_or_path: str = "sentence-transformers/paraphrase-multilingual-mpnet-base-v2",
+    batch_size: int = 32,
+    use_gpu: bool = True
 ) -> Tuple[List[float], List[float]]:
     """
     Computes Transformer-based similarity of predicted answer to gold labels to derive a more meaningful metric than EM or F1.
@@ -403,6 +405,9 @@ def semantic_answer_similarity(
     :param gold_labels: Labels as list of multiple possible answers per question
     :param sas_model_name_or_path: SentenceTransformers semantic textual similarity model, should be path or string
                                      pointing to downloadable models.
+    :param batch_size: Number of prediction label pairs to encode at once.
+    :param use_gpu: Whether to use a GPU or the CPU for calculating semantic answer similarity.
+                    Falls back to CPU if no GPU is available.
     :return: top_1_sas, top_k_sas
     """
     assert len(predictions) == len(gold_labels)
@@ -411,6 +416,8 @@ def semantic_answer_similarity(
     cross_encoder_used = False
     if config.architectures is not None:
         cross_encoder_used = any(arch.endswith("ForSequenceClassification") for arch in config.architectures)
+        
+    device = None if use_gpu else 'cpu'
 
     # Compute similarities
     top_1_sas = []
@@ -420,14 +427,14 @@ def semantic_answer_similarity(
     # Based on Modelstring we can load either Bi-Encoders or Cross Encoders.
     # Similarity computation changes for both approaches
     if cross_encoder_used:
-        model = CrossEncoder(sas_model_name_or_path)
+        model = CrossEncoder(sas_model_name_or_path, device=device)
         grid = []
         for preds, labels in zip(predictions, gold_labels):
             for p in preds:
                 for l in labels:
                     grid.append((p, l))
             lengths.append((len(preds), len(labels)))
-        scores = model.predict(grid)
+        scores = model.predict(grid, batch_size=batch_size)
 
         current_position = 0
         for len_p, len_l in lengths:
@@ -439,7 +446,7 @@ def semantic_answer_similarity(
             current_position += len_p * len_l
     else:
         # For Bi-encoders we can flatten predictions and labels into one list
-        model = SentenceTransformer(sas_model_name_or_path)
+        model = SentenceTransformer(sas_model_name_or_path, device=device)
         all_texts: List[str] = []
         for p, l in zip(predictions, gold_labels):  # type: ignore
             # TODO potentially exclude (near) exact matches from computations
@@ -447,7 +454,7 @@ def semantic_answer_similarity(
             all_texts.extend(l)
             lengths.append((len(p), len(l)))
         # then compute embeddings
-        embeddings = model.encode(all_texts)
+        embeddings = model.encode(all_texts, batch_size=batch_size)
 
         # then select which embeddings will be used for similarity computations
         current_position = 0

haystack/pipelines/base.py

@@ -696,6 +696,8 @@ class Pipeline(BasePipeline):
         documents: Optional[List[List[Document]]] = None,
         params: Optional[dict] = None,
         sas_model_name_or_path: str = None,
+        sas_batch_size: int = 32,
+        sas_use_gpu: bool = True,
         add_isolated_node_eval: bool = False,
     ) -> EvaluationResult:
         """
@@ -719,6 +721,9 @@ class Pipeline(BasePipeline):
                     - Good default for multiple languages: "sentence-transformers/paraphrase-multilingual-mpnet-base-v2"
                     - Large, powerful, but slow model for English only: "cross-encoder/stsb-roberta-large"
                     - Large model for German only: "deepset/gbert-large-sts"
+        :param sas_batch_size: Number of prediction label pairs to encode at once by CrossEncoder or SentenceTransformer while calculating SAS.
+        :param sas_use_gpu: Whether to use a GPU or the CPU for calculating semantic answer similarity.
+                            Falls back to CPU if no GPU is available.
         :param add_isolated_node_eval: If set to True, in addition to the integrated evaluation of the pipeline, each node is evaluated in isolated evaluation mode.
                     This mode helps to understand the bottlenecks of a pipeline in terms of output quality of each individual node.
                     If a node performs much better in the isolated evaluation than in the integrated evaluation, the previous node needs to be optimized to improve the pipeline's performance.
@@ -761,7 +766,8 @@ class Pipeline(BasePipeline):
                     gold_labels = df["gold_answers"].values
                     predictions = [[a] for a in df["answer"].values]
                     sas, _ = semantic_answer_similarity(
-                        predictions=predictions, gold_labels=gold_labels, sas_model_name_or_path=sas_model_name_or_path
+                        predictions=predictions, gold_labels=gold_labels, sas_model_name_or_path=sas_model_name_or_path,
+                        batch_size=sas_batch_size, use_gpu=sas_use_gpu
                     )
                     df["sas"] = sas