vllm-project/vllm · error · ValueError

Invalid backend for piecewise compilation: {self.backend}

Error message

Invalid backend for piecewise compilation: {self.backend}

What it means

Error "Invalid backend for piecewise compilation: {self.backend}" thrown in vllm-project/vllm.

Source

Thrown at vllm/config/compilation.py:1029

        enabled_ops = {op[1:] for op in self.custom_ops if op.startswith("+")}
        disabled_ops = {op[1:] for op in self.custom_ops if op.startswith("-")}
        conflicting_ops = sorted(enabled_ops & disabled_ops)
        if conflicting_ops:
            raise ValueError(
                "custom_ops cannot both enable and disable the same operation(s): "
                f"{', '.join(conflicting_ops)}. Remove either the '+' or '-' directive"
            )

        # Currently only eager and inductor backend are supported.
        # for piecewise compilation. Custom backends are not supported for
        # piecewise compilation. Update when more backends are supported.
        if self.mode == CompilationMode.VLLM_COMPILE and self.backend not in [
            "",
            "eager",
            "inductor",
        ]:
            raise ValueError(
                f"Invalid backend for piecewise compilation: {self.backend}"
            )

        # Validate encoder CUDA graph configuration
        if (
            self.cudagraph_mm_encoder
            and self.encoder_cudagraph_max_vision_items_per_batch < 0
        ):
            raise ValueError(
                "encoder_cudagraph_max_vision_items_per_batch must be "
                "non-negative (0 = auto-infer)"
            )
        if (
            self.cudagraph_mm_encoder
            and self.encoder_cudagraph_max_frames_per_batch is not None
            and self.encoder_cudagraph_max_frames_per_batch < 0
        ):
            raise ValueError(

View on GitHub (pinned to c794754062)

Solutions

1. Choose a supported piecewise compilation backend (e.g. 'inductor') instead of the current one.
2. Check CompilationConfig documentation for valid split/piecewise backends.

When it happens

Trigger: Raised at vllm/config/compilation.py:1029 when validation fails: Invalid backend for piecewise compilation. Typically triggered by an incompatible or incomplete vLLM configuration, an unsupported platform/backend combination, or a runtime resource/dependency that is missing.

Common situations: Commonly encountered at vllm/config/compilation.py:1029 during vLLM startup/config validation or runtime setup when: (1) conflicting CLI flags or config fields are combined, (2) the current platform (CUDA/ROCm/CPU/XPU) or installed optional packages do not support the requested feature, or (3) a required value is absent or out of range. Resolve by correcting the configuration as described in the message, or by selecting a supported alternative.

AI-assisted analysis of vllm-project/vllm@c794754062 (2026-08-14). Data as JSON: /api/errors/785b2071474ad1f2. Report an issue: GitHub.