Gahow Wang
4028c587b1
Adds the system-level argument resolving the roofline/PD-sep paradox. Even at 95% cache reuse prefill stays compute-bound (the C6 roofline fact), yet PD separation regresses TTFT 72%. The new system_analysis.md walks through six layers showing why the roofline claim is necessary but not sufficient, with the falsifiable condition being decode-side KV memory budget: concurrent_decode * KV_per_req / (N_D * HBM_pool). For chatbot this ratio is << 1 at any layout; for agentic at p90+ context it goes >> 1 under 4P+4D and 6P+2D, predicting the empirical 97% decode KV occupancy. fig_kv_memory_wall.pdf visualizes the model with audit-able constants; fig_c1a/b ground the per-request KV-size inputs in the actual sampled trace (input p50=33.5k, p90=101k, intra-session reuse 79.2%). Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>