Refactor attention backend (#1381)

python/sglang/srt/server_args.py

@@ -83,8 +83,8 @@ class ServerArgs:
     json_model_override_args: str = "{}"
 
     # Optimization/debug options
-    attention_backend: str = "flashinfer"
-    sampling_backend: str = "flashinfer"
+    attention_backend: Optional[str] = None
+    sampling_backend: Optional[str] = None
 
     disable_flashinfer: bool = False
     disable_flashinfer_sampling: bool = False
@@ -148,6 +148,17 @@ class ServerArgs:
             )
             self.sampling_backend = "pytorch"
 
+        # Default kernel backends
+        if self.enable_mla:
+            logger.info("MLA optimization is tunred on. Use triton backend.")
+            self.attention_backend = "triton"
+
+        if self.attention_backend is None:
+            self.attention_backend = "flashinfer"
+
+        if self.sampling_backend is None:
+            self.sampling_backend = "flashinfer"
+
         # Model-specific patches
         if "Alibaba-NLP/gte-Qwen2-1.5B-instruct" == self.model_path:
             logger.info(