{"record":{"id":"e828d6be1468e137","repo":"sgl-project/sglang","slug":"dcp-kv-mask-is-not-supported-for-fp4-kv-cache","errorCode":null,"errorMessage":"dcp_kv_mask is not supported for FP4 KV cache.","messagePattern":"dcp_kv_mask is not supported for FP4 KV cache\\.","errorType":"exception","errorClass":"RuntimeError","httpStatus":null,"severity":"error","filePath":"python/sglang/srt/mem_cache/memory_pool.py","lineNumber":2398,"sourceCode":"        cache_k: torch.Tensor,\n        cache_v: torch.Tensor,\n        k_scale: Optional[float] = None,\n        v_scale: Optional[float] = None,\n        layer_id_override: Optional[int] = None,\n        dcp_kv_mask: Optional[torch.Tensor] = None,\n    ):\n        loc, _, _ = unwrap_write_loc(loc_info)\n        # Catch stale slot ids here instead of as illegal-addr / silent KV\n        # corruption in the store_kvcache write (gated on SGLANG_ENABLE_ASYNC_ASSERT).\n        maybe_detect_oob(loc, 0, self.size + self.page_size, \"set_kv_buffer (MHA)\")\n        layer_id = (\n            layer_id_override if layer_id_override is not None else layer.layer_id\n        )\n        global_layer_id = layer.layer_id if layer is not None else layer_id\n\n        if self.is_quantized_kv_cache:\n            if dcp_kv_mask is not None:\n                raise RuntimeError(\"dcp_kv_mask is not supported for FP4 KV cache.\")\n            self._set_quantized_kv_buffer(\n                layer_id,\n                global_layer_id,\n                loc,\n                cache_k,\n                cache_v,\n                k_scale,\n                v_scale,\n            )\n            return\n\n        if cache_k.dtype != self.dtype:\n            if k_scale is not None:\n                cache_k.div_(k_scale)\n            if v_scale is not None:\n                cache_v.div_(v_scale)\n            cache_k = cache_k.to(self.dtype)\n            cache_v = cache_v.to(self.dtype)","sourceCodeStart":2380,"sourceCodeEnd":2416,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/srt/mem_cache/memory_pool.py#L2380-L2416","documentation":"Error \"dcp_kv_mask is not supported for FP4 KV cache.\" thrown in sgl-project/sglang.","triggerScenarios":"Thrown at python/sglang/srt/mem_cache/memory_pool.py:2398 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}