Segment 72

In this sub-session, the assistant definitively root-caused and fixed the persistent bf16 high-concurrency tool-call corruption in DeepSeek-V4-Flash-NVFP4 by identifying a multi-stream-overlap race during CUDA-graph capture and disabling it via environment variable, with zero code changes. The assistant then pivoted to improving decode throughput scaling from C60 to C90, rigorously investigating Two-Batch Overlap (TBO) and concluding it was infeasible due to architectural blockers, then A/B tested re-enabling the overlap scheduler on decode for a modest throughput gain but discovered a structural TP-collective desync hazard under stress, committing to a proper fix. A production incident where requests got stuck after a restart was resolved by performing a full PD co-restart, with the root cause identified as degraded NIXL bootstrap state from decode-only restarts against a long-running prefill; operational guidance was documented. Finally, the user reported a persistent hang in the session-bible tool, and analysis of a goroutine dump revealed a complete client-side deadlock with all agents stuck in HTTP calls to the LLM API, isolating the bottleneck to the HTTP layer and requiring client-side hardening with timeouts and circuit breakers.

Root-cause bf16 corruption under CUDA-graph captureFix corruption via multi-stream-overlap disableInvestigate decode throughput scaling to C90Evaluate Two-Batch Overlap feasibilityA/B test overlap scheduler on decodeFix TP-collective desync hazardResolve production PD bootstrap incidentDocument PD co-restart guidanceDiagnose session-bible tool hangIdentify HTTP-layer deadlock from goroutine dump

The Production Engineer's Playbook: Debugging Corruption, Scaling Throughput, and Surviving Incidents on Blackwell GPUs 3530 words

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