Routing fix: new sessions placed by cumulative token load (greedy bin
packing) with cache-hit tiebreak. Session affinity for turn 2+.
Replayer now sends X-Session-Id header for proper session tracking.
Agentic workload core patterns (GLM-5.1 trace):
- 91% of reusable KV is intra-session (not cross-session)
- Session-sticky routing is THE critical optimization
- 36% warm requests (1.3k new tokens), 64% cold (17k+)
- After cache: effective prefill/decode ratio drops from 61.5x to 28.7x
- Cross-session sharing (system prompt) is only 4.8% of tokens
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Systematic study of prefill-decode disaggregation for agentic LLM workloads
using production GLM-5.1 coder trace (2.1M requests, 71B input tokens).
Key findings:
- Cache-aware routing improves TPOT p90 by 15% and APC from 20.8% to 44.7%
without PD separation, matching PD-Sep's decode isolation benefit
- PD separation adds +72% TTFT overhead (KV transfer) with no TPOT gain
when using the same cache-aware scheduler
- Prefill remains compute-bound even at 95% KV cache reuse (AI >1000x
vs decode AI <2), but absolute FLOPs drop 71% from cache hits
- For agentic MoE workloads, cache-aware routing > PD separation
Infrastructure:
- Trace sampler preserving session structure + hash_ids for prefix sharing
- Async trace replayer with streaming TTFT/TPOT/E2E measurement
- Unified cache-aware + token-level load-balanced global scheduler proxy
supporting both PD-colocated and PD-disaggregated (Mooncake/RDMA) modes
- vLLM 0.18.1 scheduler patch for KV transfer abort race condition
- Roofline analysis tool for prefill/decode compute characterization
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
