V2_DEEP_ANALYSIS §3.1 (execution_mode distribution) and §3.2 (path-level
latency vs DP) had hand-typed tables with approximate latencies (e.g.
"~1.0s") and required readers to mentally compare 5+ rows × 5 columns.
Both sections now reference generated PNG figures derived directly from
the v2 + DP metrics.jsonl files.
§3.1 figure (v2_execution_mode_distribution.png):
Horizontal bar chart, log x-axis. 4076 direct-to-D fast-path requests
(green) dwarf the rest by ~30x; the long tail of slow / fallback /
failure modes is visible at one glance. Counts and percentages
annotated on each bar.
§3.2 figure (v2_path_level_latency.png):
Grouped bar chart, log y-axis. Per-path TTFT p50 / TTFT p99 / Lat p50
with exact numeric labels (no more "~1.0s" approximations). Sample
counts annotated below each path. Quick visual reads:
- KVC fast path TTFT p50 41ms vs DP 92ms (2.2x faster)
- KVC reseed TTFT p99 5.12s vs DP 0.43s (12x slower) -- the cost
- KVC no-d-capacity TTFT p99 7.65s (worst case)
Bundled:
- scripts/analysis/plot_v2_path_breakdown.py -- the script that
generates both figures; rerunable when v2 data changes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
After the critic-agent audit, V2_DEEP_ANALYSIS had drifted into an
audit-grade "5 wins / 1 loss / 3 draws" framing that mistook KVC's
deliberate design motifs (cache concentration via session affinity;
prefill-GPU idle as TTFT-stability trade-off) for "comparison
unfairness." This commit corrects the framing back to a production-
decision lens and adds a paper-track formal specification of the
router algorithm.
V2_DEEP_ANALYSIS_ZH.md changes:
- §0 TL;DR: lead with "online coding agent serving should pick
KVC 1P3D"; the only real cost is TTFT p99 long-tail (3x DP) from
the 8.3% mooncake reseed path, mitigable with real RDMA.
- §4 restructured into three buckets:
real costs (TTFT p99 tail, abort accounting now fixed),
counter-arguments to the critic (cache concentration and idle
prefill GPU are design intent, not deficits),
methodology to-do (naive-1P3D control, v2 N>=2 determinism).
- §6 replaces "5/1/3 rescoring" with production decision rationale:
KVC wins on 6 latency/TTFT metrics + lower failure rate; pays
TTFT p99 tail; lists workloads where DP would reverse the call.
- §8 decision points: D1 recommends Yes (accept v2 as milestone);
D8 added: paper motif "KVC trades P idle for TTFT stability."
KVC_ROUTER_ALGORITHM.md (new, paper-track, Chinese narrative + English
algorithm boxes / variable names / theorems for direct paper reuse):
- Problem formulation, system model, full notation
- Algorithm 1 Route: lexicographic-tuple scoring on
(overlap+alpha*sticky, sticky, -inflight, -assigned)
- Algorithm 2 Admit: D-worker autonomous admission deciding
Direct / Seed / Reseed / reject (with reason)
- Algorithm 3 Dispatch: end-to-end orchestration with reset-on-success
(the v2-specific fix that eliminates v1's self-amplifying thrashing)
- Theorem 1 (no permanent starvation) and Theorem 2 (fast-path
determinism), each with a proof sketch
- Comparison table vs vanilla pd-disagg / DP cache-aware
- Anti-patterns ("what KVC explicitly is NOT")
- Open questions for reviewers
- Suggested paper citation phrasing
- Appendix A: algorithm-step to source-file:line crosswalk
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The old filter `if row.latency_s is not None` accepted SGLang's fast
input-length-aborts (latency_s ~ 0.08s, finish_reason='abort/BadRequest')
as if they were successful zero-cost requests. This deflated mean/p50
of any run where the model rejected oversized inputs.
Impact on existing comparisons (ts=1 4-run validation + v2):
KVC v2 has 40 aborts + 5 ReadTimeouts (was reported as just 5);
DP 4w has 67 aborts (was reported as 5).
Both runs have abort behavior; the asymmetry (40 vs 67) is purely from
SGLang's mem-fraction-derived max-input-len: KVC decode-only worker gets
~10 GB free GPU mem -> max-input=92098, DP fused worker gets ~9 GB ->
max-input=87811, because DP also needs chunked-prefill workspace.
The KVC-vs-DP latency-win direction holds and widens slightly under the
fixed filter (lat mean delta: -0.8% -> -1.4%); see V2_DEEP_ANALYSIS_ZH
§4.3 for the recomputed table.
Changes:
- metrics.py: new _is_failed_request(row) helper; latency/ttft/tpot
stats now exclude both errors and aborts. New summary fields
abort_count and failure_count expose the counts directly.
- scripts/analysis/recompute_summary.py: re-derives summary.json from
existing metrics.jsonl using the fixed code, with optional --diff
against the old buggy summary for inspection.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Post-v2 audit consolidating ts=1 validation + v1 thrashing + v2 win, plus
critic-agent adversarial review of the v2 vs 4DP comparison.
Headline outcomes:
- TEAM_REPORT §1 (session pin starvation) fully fixed by v2 migration +
reset-on-success; direct-to-D 42.8% -> 91.6%.
- TEAM_REPORT §2/§3/§5 (LRU, backpressure, admission RPC) are absorbed by
ts=1 natural drain time, not mechanism-fixed -- will resurface under
ts=10/longer traces/higher concurrency.
- TEAM_REPORT §6 (ts=10 distortion) confirmed and locked as precondition;
TEAM_REPORT §8 (N=1 unreliable) rewritten to "high-pressure N>=3, normal N=1".
Three new problems exposed by adversarial review:
- TTFT p99: KVC 1.285s vs DP 0.427s (KVC 3.0x worse) -- cherry-picked out of
the V2_RESULTS_ZH.md headline table. Root cause: 8.3% non-direct path pays
3-7s mooncake reseed cost on 50-90K-token KV transfer.
- Error accounting asymmetry: DP has 67 fast-aborts (not 5) at ~0.08s each
counted in latency stats; KVC's 5 ReadTimeouts excluded entirely. Root
cause: --max-input-len 87811 (DP) vs 92098 (KVC) + metrics.py:124 filter.
- Topology mismatch: KVC 1P3D's prefill GPU is idle 91.7% of the time
(only ~373/4449 requests use seed/P path); 4DP CA has all 4 GPUs at full
utilization. Plus: no naive 1P3D control exists in the repo -- cannot
isolate KVC-layer contribution from 1P3D-topology contribution.
Re-scored headline: 5 KVC wins / 1 DP win / 3 draws -- still net positive
but not the "7/8 wins" framing the V2_RESULTS_ZH.md claims.
Recommended follow-ups (ROI order):
1. naive 1P3D ts=1 N=1 control (critic's only CRITICAL finding)
2. v2 N=2/N=3 to verify ts=1 determinism with new code paths
3. symmetric error accounting recompute + DP max-input-len = 92098 rerun
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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>
Replay-side changes paired with the SGLang admission hint:
- DecodeResidencyState gains pause_until_s; admission probe parses
recommended_pause_ms and updates the per-D pause window.
- _wait_for_decode_pause is invoked at request entry points
(_invoke_router, _invoke_session_direct) so requests stall before
hitting a saturated D instead of timing out via mooncake.
- New CLI flags: --enable-backpressure (default off, baseline preserved),
--backpressure-max-pause-s (cap on per-request sleep, default 2s).
Structural instrumentation written under <run_dir>/structural/:
- admission-events.jsonl: every admission probe (RTT, queue_depth,
pause_ms, available_tokens, evicted_count)
- backpressure-events.jsonl: every actual pause sleep
- session-d-binding.jsonl: per-request policy decision
Used to validate the structural claims documented separately.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Add `recommended_pause_ms` field to DirectAppendAdmissionReqOutput so D
can advise callers when its transfer queue is heavy or KV pool is near
capacity. The hint is computed from transfer_queue_depth,
retracted_queue_depth, and post-trim token_usage; thresholds are simple
heuristics (>0.90 usage, >=8 queue depth, retracted>0).
Default behavior is unchanged for callers that ignore the field.
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 dropped errors but pushed session-cap fallback to 46-51%. Before adding
v6 mitigations we need to attribute that capacity loss to one of:
(a) active sessions — real footprint
(b) idle-evictable sessions — LRU not aggressive enough
(c) prefill backup blocks / in-flight / fragmentation — release timing
Without this it's all guessing. Plumb a 1Hz poller into replay that hits
each P/D worker's /server_info, captures session_cache + memory_usage, and
writes a per-worker time-series JSONL to <run_dir>/d-pool-timeseries.jsonl.
Off by default (--pool-poll-interval-s 0); v5+profile sweep enables it at
1.0s. Per-tick HTTP cost is ~8 parallel /server_info calls — negligible
relative to the 50min run.
Analyzer (scripts/analysis/analyze_pool_timeseries.py) decomposes each D's
capacity into active_held / idle_evictable / other (= cap-held-avail, the
backup-blocks bucket) / free, and reports session residency churn across
workers as a starvation/thrashing signal.
Mock-tested poller end-to-end (cancellation clean, file flushed, sessions
captured); analyzer validated against synthetic timeseries.
Next: run scripts/sweep_tp1_v5_optD_profile.sh on hardware (~90min), then
analyze results to pick a v6 direction.
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>
v4 (cap=16) saw 35% session-cap fallback because the local soft_cap
min(16, usable / target) evaluates to 1-2 for large agentic inputs.
The cap was hit not because D was full but because replay's heuristic
underestimated capacity.
This change makes worker admission_mode authoritative for ALL paths:
SGLang side:
- io_struct.py: DirectAppendAdmissionReqInput gains a `mode` field
("direct_append" | "seed", default "direct_append" preserves prior
behavior).
- scheduler.py:admit_direct_append: when mode == "seed", skip the
resident-on-D requirement and run the same capacity check + LRU
eviction (maybe_trim_decode_session_cache) that direct_append uses.
This lets D atomically decide if a new session can be admitted based
on actual token_to_kv_pool_allocator state.
Replay side (replay.py):
- _query_decode_direct_admission gains a `mode` parameter.
- _reserve_decode_session_capacity: in worker admission_mode, the
seed/reseed branch now queries D with mode="seed" and trusts the
result, instead of estimating capacity from the residency snapshot.
- _should_admit_new_decode_session: in worker mode, skip the local
soft_cap pre-check and let D decide. Same-D session fast-path is
preserved.
Effects:
- Local hardcoded cap of 16 is bypassed under worker mode; D's real
KV pool size is the only constraint.
- LRU eviction runs in D's process atomically with admission, so
starvation (the v3 bimodal "lucky vs starved sessions" pattern)
should resolve.
scripts/sweep_tp1_v5_optD.sh added to run the same 1P7D / 2P6D
configs as v4 with the new admission path.
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>
