Chunk 62.1

After successfully deploying the native SGLang DFlash environment on CT200, the assistant moved to enable actual DDTree tree verification (non-shadow mode) by adding `--speculative-ddtree-allow-hybrid-unsafe` to bypass the safety gate for Qwen3.6’s hybrid recurrent layers. Initial attempts with budget=16 showed coherent output but lower throughput than DFlash linear due to the overhead of per‑depth top‑k logprob computation and mamba state leakage at sibling tree nodes. By tuning the budget to 15 (matching the verify block size to linear’s 16 tokens) and capping the top‑k to 8, the assistant achieved a configuration where DDTree frequently accepts the full 15‑draft depth, yielding a **24% throughput improvement** over DFlash linear (124.2 vs 100.1 tok/s average across five diverse prompts). The best single‑prompt result was **174.1 tok/s on a JSON parsing task** (2.1× linear). The user then requested a more extensive evaluation: benchmarking at TP4 and TP8, sweeping draft budgets, simulating agentic multi‑turn workloads, and producing a LaTeX report with charts. The assistant responded by writing `bench-plan.md`, a detailed plan covering eight speculative decoding methods (autoregressive, DFlash linear, DDTree at six budgets), three tensor‑parallel configurations (1/4/8 GPUs), five workload types (short, long, very long, two agentic multi‑turn scenarios), and a concurrency sweep. The plan outlines a structured LaTeX report with six sections, pgfplots grouped bar charts, line plots, and error bars, with an estimated total run time of ~2.5 hours on CT200’s eight RTX PRO 6000 Blackwell GPUs. The overall theme of this chunk is **transitioning from environment bootstrapping to systematic performance validation and planning**. The assistant resolved the key technical blocker (hybrid model state leakage) through empirical tuning, demonstrated a clear speedup over the baseline, and then pivoted to designing a rigorous, multi‑dimensional benchmark suite to quantify DDTree’s advantages across realistic deployment scenarios. The work establishes a reproducible methodology for evaluating speculative decoding on high‑end Blackwell hardware.

From Silent Crash to 24% Improvement: The DDTree Deployment Journey on CT200 2503 words

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