sgl-project/sglang · error · ValueError

--prefill-decode-interval must be non-negative.

Error message

--prefill-decode-interval must be non-negative.

What it means

Raised by _validate_prefill_decode_interval when --prefill-decode-interval is negative. The interval controls how often the scheduler alternates between prefill and decode; negative intervals are invalid (0 means interleave every step).

Source

Thrown at python/sglang/srt/server_args.py:9567

    def _handle_asr_validation(self):
        """Validate transcription/ASR-specific server args."""
        cfg = resolving_view(self)
        if cfg.asr_max_buffer_seconds <= 0:
            raise ValueError(
                f"--asr-max-buffer-seconds must be positive "
                f"(got {cfg.asr_max_buffer_seconds})."
            )
        if cfg.asr_max_concurrent_sessions <= 0:
            raise ValueError(
                f"--asr-max-concurrent-sessions must be positive "
                f"(got {cfg.asr_max_concurrent_sessions})."
            )

    def _validate_prefill_decode_interval(self):
        cfg = resolving_view(self)
        if cfg.prefill_decode_interval < 0:
            raise ValueError("--prefill-decode-interval must be non-negative.")

    def _handle_other_validations(self):
        cfg = resolving_view(self)
        if cfg.default_chat_template_kwargs is not None and not isinstance(
            cfg.default_chat_template_kwargs, dict
        ):
            raise ValueError(
                "--default-chat-template-kwargs must decode to a JSON object"
            )

        # Handle optimistic prefill validation
        if cfg.optimistic_prefill_attempts > 0 and cfg.disaggregation_mode == "prefill":
            if cfg.pp_size > 1:
                logger.warning("Optimistic prefill does not support pp_size > 1")
                self._declare(
                    "_handle_other_validations",
                    optimistic_prefill_attempts=0,
                )

View on GitHub (pinned to 0132848349)

Solutions

1. Use 0 or a positive value; use a large value (e.g. 1000000) to effectively disable interleaving
2. Check for sign errors in generated launch commands

Example fix

# before
--prefill-decode-interval -1
# after
--prefill-decode-interval 0

if args.prefill_decode_interval is not None and args.prefill_decode_interval < 0:
    raise SystemExit('prefill_decode_interval must be >= 0')

When it happens

Trigger: Launching with a negative --prefill-decode-interval value.

Common situations: Trying to 'disable' the alternation with -1 instead of a large value; sign typos in scripted configs.

Related errors

• Decode context parallel size (--dcp-size / --decode-context-
• --mamba-max-states-per-path must be -1 (unlimited) or a posi
• --swa-full-tokens-ratio should be in range (0, 1.0].
• --asr-max-buffer-seconds must be positive (got {cfg.asr_max_
• --asr-max-concurrent-sessions must be positive (got {cfg.asr

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/a75ab1439b7fa6c4. Report an issue: GitHub.