[V32/GLM5] Change default setting of V32 nvfp4 on TP4 (#20086)

python/sglang/srt/server_args.py

@@ -1279,7 +1279,9 @@ class ServerArgs:
             )
 
         if self.kv_cache_dtype == "auto":
-            self.kv_cache_dtype = "fp8_e4m3" if major >= 10 else "bfloat16"
+            self.kv_cache_dtype = (
+                "fp8_e4m3" if (major >= 10 and self.dp_size > 1) else "bfloat16"
+            )
             logger.warning(
                 f"Setting KV cache dtype to {self.kv_cache_dtype} for DeepSeek DSA on SM{major} device."
             )
@@ -1298,11 +1300,18 @@ class ServerArgs:
             self.nsa_prefill_backend = "tilelang"
             self.nsa_decode_backend = "tilelang"
         elif kv_cache_dtype == "fp8_e4m3":
-            # flashmla_auto dispatches to flashmla_sparse/flashmla_kv based on hardware and heuristics
-            if not user_set_prefill:
-                self.nsa_prefill_backend = "flashmla_auto"
-            if not user_set_decode:
-                self.nsa_decode_backend = "flashmla_kv"
+            if self.dp_size == 1 and major >= 10:
+                self.nsa_prefill_backend = "trtllm"
+                self.nsa_decode_backend = "trtllm"
+                logger.warning(
+                    "Flashmla is not supported on Blackwell device without DP attention. Set NSA prefill/decode backends to trtllm, which runs fast but loses a little accuracy."
+                )
+            else:
+                # flashmla_auto dispatches to flashmla_sparse/flashmla_kv based on hardware and heuristics
+                if not user_set_prefill:
+                    self.nsa_prefill_backend = "flashmla_auto"
+                if not user_set_decode:
+                    self.nsa_decode_backend = "flashmla_kv"
         else:
             # set prefill/decode backends based on hardware architecture.
             if major >= 10: