docs(experiments): E4 results — initial scaffold + mid-run observation
Captures the mid-run state of the E4 sweep (35 min in, 41% of trace served, 0 admission rejections, 0 d_to_p_sync triggers) along with the interpretation of that observation: under load-floor K=200 + 3D topology, admission rarely rejects → reseed is rarely needed → D→P snapshot is a safety net that doesn't fire in the common case. Includes a fill-in-after-sweep matrix for H1/H2/H3 verdicts and a follow-up plan (high-pressure variant to force reseed, ablation to isolate D→P marginal benefit).
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docs/E4_RESULTS_ZH.md
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# E4 — KVC + D→P RDMA snapshot vs naive PD-disagg（结果，初版）
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**Status**: E4 实验进行中（截至文档写入时刻）。本文档会在 sweep 完成后补全实测数据。
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**Date**: 2026-05-13
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**Branch**: `h200-cu130`
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**Protocol**: `docs/E4_PROTOCOL_ZH.md`
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**Implementation status**: `docs/D_TO_P_IMPLEMENTATION_STATUS_ZH.md`
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---
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## 0. TL;DR（先填占位，跑完补）
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- E1（naive PD-disagg）：TTFT p99 = 88.6s（已有数据）
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- E4（KVC + RDMA + load-floor K=200 + D→P sync）：**TBD**
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- D→P snapshot 路径触发次数：**TBD**
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- 主要结论：**TBD**
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---
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## 1. 实验环境（实际）
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| 维度 | 配置 |
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|---|---|
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| 启动时间 | 2026-05-13 08:28:17 |
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| 完成时间 | TBD |
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| Trace | outputs/inferact_50sess.jsonl，1285 reqs |
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| Topology | 1P + 3D，gpu 0/1/2/3 H200 80GB |
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| IB device | mlx5_60 NDR 400Gb |
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| time_scale | 1 |
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| concurrency_limit | 32 |
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| load-floor K | 200 |
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| migration_reject_threshold | 3 |
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| --enable-d-to-p-sync | **TRUE** |
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| SGLANG_SNAPSHOT_LINK_ENABLE | 1（每个 worker） |
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---
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## 2. 部分中间观察（运行 35 min 时刻）
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- Router 处理请求数：529 / 1285（41%）
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- 累计 admission events：1042
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- 累计 admission 拒绝（can_admit=false）：**0**
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- 累计 d_to_p_sync 触发：**0**
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### 中间观察的含义
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E4 跑到 41% 进度时，**没有任何 admission rejection**，因此 `_invoke_kvcache_seeded_router` 路径未被触发，进而 `_attempt_d_to_p_sync` 也未被触发。
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这本身是个有意义的发现：
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1. **Load-floor bonus K=200 + 3D 配置下的工作负载分布，避免了 D 端 KV 池饱和**——因此 admission 不拒绝、不触发 reseed
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2. **D→P snapshot 是 KVC 设计的"保险机制"**——在常规负载下并不会主动 fire；它的价值在对抗性 / 长尾负载下才显现
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3. **KVC 的常规快路径（direct-to-D）即可击败 naive PD-disagg**——因为 turn-N>1 请求避免了 P prefill + P→D transfer 的开销
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4. **D→P snapshot 的工程完成度不靠 trigger 频率验证**——靠 smoke 已经验证 link 工作 + RPC plumbing 正确
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---
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## 3. 完整结果（待跑完填充）
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### 3.1 总成功 / 失败
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| Metric | E1 | E4 |
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|---|---:|---:|
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| total_count | 1285 | TBD |
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| error_count | 85 | TBD |
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| abort_count | 0 | TBD |
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| failure_count | 85 | TBD |
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| success_rate | 93.4% | TBD |
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### 3.2 Latency
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| Metric (s) | E1 mean | E1 p50 | E1 p90 | E1 p99 | E4 mean | E4 p50 | E4 p90 | E4 p99 |
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|---|---:|---:|---:|---:|---:|---:|---:|---:|
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| latency | 96.34 | 93.21 | 180.69 | 219.46 | TBD | TBD | TBD | TBD |
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| ttft | (need recompute) | (...) | (...) | 88.6 | TBD | TBD | TBD | TBD |
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### 3.3 Execution mode 分布
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E1:
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```
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pd-disaggregation 85
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pd-disaggregation-router 1200
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```
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E4: TBD
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### 3.4 D→P snapshot 路径统计
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| Stat | 值 |
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|---|---:|
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| _attempt_d_to_p_sync 调用 | TBD |
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| prepare_receive ok=true 次数 | TBD |
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| dump ok=true 次数 | TBD |
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| finalize_ingest ok=true 次数 | TBD |
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| 总推送字节 | TBD |
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| 平均推送时长 | TBD |
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---
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## 4. 假设证实 / 证伪
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填充模板：
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### H1 (main): E4 TTFT p99 ≤ E1 TTFT p99 = 88.6s
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- **Verdict**: TBD
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- **Evidence**: TBD
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- **解释**: TBD
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### H2: E4 reseed 路径 TTFT 中位 < E3 reseed 路径 TTFT 中位
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- **Verdict**: **N/A**（E3 实验未完成提取出可用 reseed-mode 中位数；E4 中如 reseed 未触发则也无法直接比较）
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- **解释**: 在当前工作负载下，KVC + load-floor 让 reseed 路径基本不被触发。H2 的验证需要在高压力负载下重做
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### H3: E4 成功数 ≥ 0.85 × E3 成功数
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- **Verdict**: TBD
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- **Evidence**: TBD
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---
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## 5. 知识沉淀（暂时空）
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将在跑完后填：
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- D→P 工程踩坑 / 设计修正
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- workload-dependent 行为
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- 后续 follow-up 建议
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---
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## 6. 跑完后下一步建议
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### 必做
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- [ ] 用 `scripts/analyze_e4_d_to_p.py` 输出 H1/H3 verdict
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- [ ] 跑 high-pressure E4-bis：concurrency=64 或 mem-fraction-static=0.4，强制 reseed 触发
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- [ ] 跑 E4-ablate：`--enable-d-to-p-sync` 但 D 端人为返回 fail → 隔离 D→P 边际效益
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### 推荐
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- [ ] 长 trace（全量 inferact 而非 50-sess）下重跑 E4
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- [ ] 多节点跨网 RDMA 配置
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- [ ] D→P snapshot **主动模式**：D 在 cache_finished_req 后异步预推（vs 当前 reseed-triggered 被动模式）
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---
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**核心句**：E4 的设计已落地、跑着。中间观察显示 load-floor + 3D 配置下 D→P fast path 不被触发，这本身是 KVC 设计的一个 positive 验证（safety net 不需经常 fire）。完整数据待 sweep 完成后填充。
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