fix: Add default value for backend in sample_mmmu_requests (#12256)

python/sglang/bench_serving.py

@@ -1014,7 +1014,7 @@ async def get_mooncake_request_over_time(
 def sample_mmmu_requests(
     num_requests: int,
     processor: AutoProcessor | AutoTokenizer,
-    backend: str,
+    backend: str = "sglang",
     fixed_output_len: Optional[int] = None,
     random_sample: bool = True,
 ) -> List[DatasetRow]:
@@ -1369,7 +1369,10 @@ def create_mm_data_row(
         )["input_ids"].numel()
     except Exception:
         # Fallback: just tokenize the text prompt directly
-        text_prompt_len = len(processor.tokenizer.encode(text_prompt))
+        tokenizer_to_use = (
+            processor.tokenizer if hasattr(processor, "tokenizer") else processor
+        )
+        text_prompt_len = len(tokenizer_to_use.encode(text_prompt))
 
     # Vision tokens = total tokens - text tokens
     vision_prompt_len = prompt_len - text_prompt_len