Three new docs covering the structural-fit investigation:
- AGENTIC_FIT_ANALYSIS_ZH.md: §1-§7 of structural design issues that
surface KVC vs vanilla DP gap on real agentic workloads (SWE 50sess).
Quantifies session pinning, LRU shortfall, P-side imbalance,
time-scale distortion, etc., with code citations and N=3 rerun data.
- REFACTOR_PLAN_ZH.md: KISS-edition refactor plan. After verifying the
original "estimate inflation" and "resident_blocks aging" claims were
not real bugs, scope shrinks to one code change (backpressure) plus a
4-run smoke sweep within an 8h budget.
- STRUCTURAL_VALIDATION_REPORT_ZH.md: validates §1-§7 claims using
existing v5 baseline rerun data + 8DP CA baseline. Each claim labeled
fully-supported / indirect / retracted with the data source. Notes
that backpressure E2E validation is pending GPU smoke run.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Hostile audit of the original report flagged three load-bearing errors:
1. held_tokens semantic was inverted. session_held_tokens() at
session_aware_cache.py:278-282 sums (kv_allocated_len - cache_protected_len)
per slot, i.e. slot-private (NOT in radix tree). So "other = cap - held -
avail" actually CONTAINS the radix-tree protected prefix cache (likely the
single biggest component for shared agentic prefixes), not just running
batch + in-flight as the original report claimed.
2. Admission-race causal hypothesis for the 415 EXP2+profile errors is
contradicted by the data: 414/415 errors have kv_transfer_blocks > 0 — they
passed admission and died downstream ("generate stream ended before
producing any token", raised by the client when a 200 response had an empty
stream).
3. Polling deconfound was too quickly dismissed. Mode counts shift ~1:1
(session-cap-fb -356 / kvcache-centric +406), and /server_info is not a
passive read — it dispatches into the scheduler main loop and iterates
every session slot.
Plus: per-D error% confounded by sticky session affinity (only 18 unique
sessions cause 415 errors, decode-3 had 0 errors only because no high-error
session landed there); decile 10 "recovery" was an equal-time binning
artifact (24.5% under equal-count); v5 vs v5+profile time gap was 21h not
6h; p50/p90 latency comparison is N=1.
Rewritten report (docs/V5_PROFILE_INVESTIGATION_ZH.md) marks each correction
with ⚠️ and demotes admission-race to one of four hypotheses (H1-H4).
Action items split into P0 (verify, must do first) and P1 (instrument):
P0 — scripts/sweep_tp1_v5_baseline_rerun_exp2.sh runs 3x v5 baseline EXP2
(no polling, identical config to the original v5 run) to test whether the
9-error baseline result is reproducible. If 3 runs give ~9 errors and
profile gives 415, polling is the leading suspect. Currently running
in background.
P1 — scheduler.py:_compute_pool_breakdown_for_diagnostics adds a read-only
"pool_breakdown" dict to /server_info covering: radix_evictable_tokens,
radix_protected_tokens, slot_private_held_tokens, session_slot_count,
running_batch_{reqs,kv_tokens}, transfer_queue_{reqs,tokens},
prealloc_queue_{reqs,tokens}, retracted_queue_{reqs,tokens}. With these,
"unaccounted = cap - sum(known)" exposes true leakage. replay.py captures
all fields into the per-tick row; analyzer prints the decomposition and
gracefully handles old timeseries (prints "P1 instrument absent").
Mock-tested end-to-end. SGLang patch is read-only and does not affect
admission/scheduling. Old v5+profile data still analyzes correctly.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
v5 sweep (sweep_tp1_v5_optD.sh) lands the previously-deferred Option D:
worker admission_mode authoritative for direct_append + seed + reseed,
bypassing replay's local _decode_session_soft_cap.
Key findings now documented:
- errors collapse from 9-10% to 0.2% (mooncake timeouts gone)
- session-cap fallback rises 33-35% -> 46-51% — D's true KV pool is the
binding constraint, not replay's estimator; v4's "low fallback" was
hiding capacity overruns as transfer-timeout errors
- direct-to-D subset latency unchanged from v4 (admission overhead negligible)
- new bottleneck: D's physical KV pool — points v6 at prefill backup release
timing, priority eviction tuning, chunked seed, cross-D session migration,
and real RDMA
Also adds a 5th lesson on errors-vs-fallback reciprocity and updates the
code index with the v5 endpoint extension and new CLI knobs.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Add v4 sweep results and post-mortem analysis showing:
- direct-to-D path: 54.3% (1P7D) / 58.0% (2P6D) of requests now use
KVC cleanly. P50=0.5s and TTFT P50=0.043s; this path beats baseline
8DP across the board (P50 -24%, TTFT P50 -54%, TTFT P90 -79%).
- Overall vs baseline (errors+truncated excluded):
v4 2P6D P50=0.85s vs baseline 0.66s (28% slower).
Reason is not errors -- 35% of requests still hit
fallback-large-append-session-cap, where capacity-based
cap = usable_tokens / target_tokens evaluates to 1-2 (not 16)
for large agentic inputs.
- 9-10% errors on KVC variants are mooncake TCP transfer timeouts,
not SGLang logic bugs. Prefill log shows
"Failed to send kv chunk ... 32s timeout ... session not alive".
Errors concentrate in turn>=31 (large inputs) after run >44.8%.
Track:
- docs/KVC_DEBUG_JOURNEY_V1_TO_V4.md: append v4 results table,
per-mode breakdown, and error root cause.
- scripts/analysis/{analyze_v3,analyze_v4,analyze_errors,compare_no_error}.py
- outputs/qwen3-30b-tp1-v{3,4}*/exp*_summary.json (force-added,
small JSON; metrics.jsonl excluded due to size).
- outputs/qwen3-30b-tp1-v{3,4}*/sweep_results.txt
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Document the iterative debugging from v1 (broken KVC) through v4
(routing fixed + session cap raised), with code-level analysis of
the two main bugs encountered:
1. v2 root cause (mis-diagnosed previously as `allow_local_prefill`):
`--policy default` for KVC mechanism caused replay's round-robin
policy and the PD router's round-robin to diverge, sending requests
with `session_params` to a D worker that did not have the session
open. Resulted in 56-61% truncation with finish_reason
"session id X does not exist".
Fix: use `--policy kv-aware` (sweep_tp1_v3_kvaware.sh) so replay
emits `x-smg-target-worker` and PD router uses consistent_hashing.
2. v3 new bottleneck: `pd-router-fallback-large-append-session-cap`
dominated 52-65% of requests. Root cause was hardcoded
`min(4, ...)` in `_decode_session_soft_cap`. With 7 D workers x 4
sessions = 28 slots for 52 trace sessions, ~24 sessions starved
permanently (bimodal direct-to-D rate of 0% or 99%).
Fix: raise the cap to 16 (replay.py).
Also includes the v3 finding that direct-to-d-session path P50=0.495s
and TTFT P50=0.043s already beats the 8-way DP baseline (0.65s/0.093s)
- the KVC core mechanism works when fallback paths are avoided.
Files:
- docs/KVC_DEBUG_JOURNEY_V1_TO_V4.md: full journey + code location index
- docs/SWEBENCH_EXPERIMENT_{PROGRESS,RESULTS}.md: prior session notes
- scripts/sweep_tp1_v{2,3,4}*.sh: experiment driver scripts
- src/agentic_pd_hybrid/replay.py: cap 4 -> 16, audit fields
- src/agentic_pd_hybrid/pd_router.py: strip session_params from prefill
- src/agentic_pd_hybrid/metrics.py: truncated_request_count
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
