{"record":{"id":"6fa3a07f97dabae1","repo":"sgl-project/sglang","slug":"ring-attention-requires-one-of-the-ring-capable-ba","errorCode":null,"errorMessage":"Ring Attention requires one of the ring-capable backends ({', '.join(RING_CAPABLE_ATTENTION_BACKENDS)}), got {self.attention_backend!r}","messagePattern":"Ring Attention requires one of the ring-capable backends \\((.+?)\\), got (.+?)","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"python/sglang/multimodal_gen/runtime/server_args/server_args.py","lineNumber":980,"sourceCode":"            self.backend != Backend.DIFFUSERS\n            and isinstance(self.pipeline_config, MiniMaxH3PipelineConfig)\n            and self.attention_backend == \"laser_attn\"\n            and \"text_encoder\" not in self.component_attention_backends\n        ):\n            # Laser Attention is used only by the MiniMax-H3 transformer.\n            # SDPA is faster than Ascend FA for its Qwen3-VL text encoder.\n            logger.info(\n                \"Automatically set torch_sdpa backend for the MiniMax H3 text \"\n                \"encoder; laser_attn applies to the transformer\"\n            )\n            self.component_attention_backends[\"text_encoder\"] = \"torch_sdpa\"\n\n        if self.ring_degree > 1:\n            if (\n                self.attention_backend is not None\n                and self.attention_backend not in RING_CAPABLE_ATTENTION_BACKENDS\n            ):\n                raise ValueError(\n                    \"Ring Attention requires one of the ring-capable backends \"\n                    f\"({', '.join(RING_CAPABLE_ATTENTION_BACKENDS)}), got \"\n                    f\"{self.attention_backend!r}\"\n                )\n            if self.attention_backend is None:\n                self.attention_backend = RING_CAPABLE_ATTENTION_BACKENDS[0]\n                logger.info(\n                    \"Ring Attention requires a ring-capable backend; \"\n                    \"attention_backend has been automatically set to %s\",\n                    self.attention_backend,\n                )\n\n        if self.attention_backend is None and self.backend != Backend.DIFFUSERS:\n            if (\n                current_platform.is_cuda()\n                and self.pipeline_class_name is None\n                and self.num_gpus == 1\n                and self.tp_size == 1","sourceCodeStart":962,"sourceCodeEnd":998,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/multimodal_gen/runtime/server_args/server_args.py#L962-L998","documentation":"When ring_degree > 1, the selected attention_backend must be one of RING_CAPABLE_ATTENTION_BACKENDS; any explicitly set non-ring backend raises. If unset, it defaults to the first ring-capable backend.","triggerScenarios":"ServerArgs(ring_degree=2, attention_backend='flashinfer') where 'flashinfer' is not in RING_CAPABLE_ATTENTION_BACKENDS; mixing a Ring Attention launch with a backend that lacks ring support.","commonSituations":"Reusing a single-GPU config (with a pinned attention backend) for a multi-node ring setup; upgrading when the ring-capable list changed so a previously valid backend was dropped.","solutions":["Remove the explicit attention_backend and let it default to RING_CAPABLE_ATTENTION_BACKENDS[0]","Or set attention_backend to one of the values listed in the error message","Check RING_CAPABLE_ATTENTION_BACKENDS in server_args.py for your version's supported set"],"exampleFix":"# before\nServerArgs(ring_degree=2, attention_backend=\"flashinfer\")\n# after\nServerArgs(ring_degree=2)  # auto-selects first ring-capable backend","handlingStrategy":"validation","validationCode":"if cfg.get('ring_degree', 1) > 1 and cfg.get('attention_backend') not in (None, *RING_CAPABLE_ATTENTION_BACKENDS):\n    del cfg['attention_backend']  # let the default ring-capable backend kick in","typeGuard":"def backend_supports_ring(b) -> bool:\n    return b in RING_CAPABLE_ATTENTION_BACKENDS","tryCatchPattern":null,"preventionTips":["Don't pin attention_backend in shared configs used by both single-GPU and ring deployments","Re-check RING_CAPABLE_ATTENTION_BACKENDS after upgrades"],"tags":["ring-attention","attention-backend","distributed","config-validation"],"backgroundTag":"unsupported-backend-combination","analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}