Add explicit disable flag for FlashInfer allreduce fusion (#21446)

python/sglang/srt/server_args.py

@@ -518,6 +518,7 @@ class ServerArgs:
     moe_runner_backend: str = "auto"
     flashinfer_mxfp4_moe_precision: Literal["default", "bf16"] = "default"
     enable_flashinfer_allreduce_fusion: bool = False
+    enforce_disable_flashinfer_allreduce_fusion: bool = False
     enable_aiter_allreduce_fusion: bool = False
     deepep_mode: Literal["auto", "normal", "low_latency"] = "auto"
     ep_num_redundant_experts: int = 0
@@ -2082,6 +2083,14 @@ class ServerArgs:
                 f"Auto-enabling FlashInfer AllReduce Fusion on SM90/SM10X for {model_arch}"
             )
 
+        # Apply enforce_disable_flashinfer_allreduce_fusion after all model-specific adjustments
+        if self.enforce_disable_flashinfer_allreduce_fusion:
+            self.enable_flashinfer_allreduce_fusion = False
+            logger.info(
+                "FlashInfer allreduce fusion is forcibly disabled "
+                "via --enforce-disable-flashinfer-allreduce-fusion."
+            )
+
     def _handle_mamba_radix_cache(
         self,
         model_arch: str,
@@ -4874,6 +4883,11 @@ class ServerArgs:
             action="store_true",
             help="Enable FlashInfer allreduce fusion with Residual RMSNorm.",
         )
+        parser.add_argument(
+            "--enforce-disable-flashinfer-allreduce-fusion",
+            action="store_true",
+            help="Enforce disable FlashInfer allreduce fusion.",
+        )
         parser.add_argument(
             "--enable-aiter-allreduce-fusion",
             action="store_true",