fix: improve find_segments via numpy diff (#2686)

server/text_generation_server/utils/segments.py

@@ -5,30 +5,25 @@
 from typing import List, Tuple, Union
 
 import torch
+import numpy as np
 
 
-# FIXME: this should be optimized
 def find_segments(
     adapter_indices: Union[torch.Tensor, List[int]]
 ) -> Tuple[List[int], List[int]]:
-    segments = [0]
-    segment_indices = []
-
     if isinstance(adapter_indices, torch.Tensor):
-        # Calling .item() repeatedly on CUDA tensor is very slow, so we move it to CPU first
-        adapter_indices = adapter_indices.cpu().tolist()
+        adapter_indices = adapter_indices.cpu().numpy()
+    elif isinstance(adapter_indices, list):
+        adapter_indices = np.array(adapter_indices)
 
-    start_index = 0
-    for i in range(1, len(adapter_indices)):
-        if adapter_indices[i] != adapter_indices[i - 1]:
-            segments.append(i)
-            segment_indices.append(adapter_indices[i - 1])
-            start_index = i
+    change_mask = np.diff(adapter_indices, prepend=adapter_indices[0] - 1)
+    change_indices = np.nonzero(change_mask)[0]
+
+    segments = [0]
+    segments.extend(change_indices[1:].tolist())
+    segments.append(len(adapter_indices))
 
-    # Handle the last segment
-    if start_index < len(adapter_indices):
-        segments.append(len(adapter_indices))
-        segment_indices.append(adapter_indices[-1])
+    segment_indices = adapter_indices[change_indices].tolist()
 
     return segments, segment_indices