[Core] Use numpy to speed up padded token processing (#6442)

vllm/model_executor/sampling_metadata.py

@@ -2,6 +2,7 @@ import random
 from dataclasses import dataclass
 from typing import Dict, List, Optional, Tuple
 
+import numpy as np
 import torch
 
 from vllm.model_executor.layers.ops.sample import get_num_triton_sampler_splits
@@ -457,16 +458,20 @@ class SamplingTensors:
         if do_penalties:
             prompt_max_len = max([len(tokens) for tokens in prompt_tokens],
                                  default=0)
-            prompt_padded_tokens = [
-                tokens + [vocab_size] * (prompt_max_len - len(tokens))
-                for tokens in prompt_tokens
-            ]
+            prompt_padded_tokens = np.full(
+                (len(prompt_tokens), prompt_max_len),
+                vocab_size,
+                dtype=np.int64)
+            for i, tokens in enumerate(prompt_tokens):
+                prompt_padded_tokens[i, :len(tokens)] = tokens
             output_max_len = max([len(tokens) for tokens in output_tokens],
                                  default=0)
-            output_padded_tokens = [
-                tokens + [vocab_size] * (output_max_len - len(tokens))
-                for tokens in output_tokens
-            ]
+            output_padded_tokens = np.full(
+                (len(output_tokens), output_max_len),
+                vocab_size,
+                dtype=np.int64)
+            for i, tokens in enumerate(output_tokens):
+                output_padded_tokens[i, :len(tokens)] = tokens
 
         temperatures_t = torch.tensor(
             temperatures,
@@ -517,18 +522,11 @@ class SamplingTensors:
             pin_memory=pin_memory,
         )
         if do_penalties:
-            prompt_tensor = torch.tensor(
-                prompt_padded_tokens,
-                device="cpu",
-                dtype=torch.long,
-                pin_memory=pin_memory,
-            )
-            output_tensor = torch.tensor(
-                output_padded_tokens,
-                device="cpu",
-                dtype=torch.long,
-                pin_memory=pin_memory,
-            )
+            prompt_tensor = torch.from_numpy(prompt_padded_tokens)
+            output_tensor = torch.from_numpy(output_padded_tokens)
+            if pin_memory:
+                prompt_tensor = prompt_tensor.pin_memory()
+                output_tensor = output_tensor.pin_memory()
         else:
             prompt_tensor = None
             output_tensor = None