[Feature][KVCache] Add per-head SWA block recycle to ResourceManagerV1 (Hackathon 10th Spring No.53)

[johnny-cloudforge]

PR1 Body — [Feature][KVCache] Add per-head SWA block recycle to ResourceManagerV1 (Hackathon 10th Spring No.53)

Push-ready version (all commits staged, bench gate passed). Saved here, not in /tmp.
5 required sections per FastDeploy CI gate. Word budget ≤600.

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Motivation

Hackathon 10th Spring Task No.53 — 离散 KV Cache 管理和 AppendAttention 算子的性能优化 (PR1 of 2). Spec: https://github.com/PaddlePaddle/community/blob/master/hackathon/hackathon_10th/【Hackathon_10th】开源贡献个人挑战赛春节特别季—任务合集.md#no53.

For models that mix Sliding-Window Attention (SWA) heads with full-attention heads inside the same layer, today's V1 KV-cache scheduling path (ResourceManagerV1 + PrefixCacheManager, gated by the default-on ENABLE_V1_KVCACHE_SCHEDULER=1) allocates one shared block_idx per layer for all heads. SWA heads finish their window long before full-attn heads, but their cache stays pinned until the whole layer evicts. Throughput suffers.

This PR teaches the V1 scheduler + PrefixCacheManager to manage block_idx per head (head-wise SWA layout) and recycle a SWA head's cache as soon as it crosses its window — the per-head equivalent of what PR #6702 did for V0.

Authorship: this PR is independently designed and implemented by the submitter for Hackathon 10th Spring No.53. The earlier community PR #6702 (V0, not merged) is referenced as prior art only; no code is lifted unattributed. Any future contributor work will be acknowledged via per-commit Co-authored-by trailers.

RFC: PaddlePaddle/community#1361.

Modifications

Area	Change
fastdeploy/cache_manager/prefix_cache_manager.py	Per-request head-wise GPU free list (gpu_free_block_list_head_wise[head]); allocate_gpu_blocks_head_wise / recycle_gpu_blocks_head_wise; TP-aware sizing (num_key_value_heads // tp_size)
fastdeploy/engine/sched/resource_manager_v1.py	recycle_request_swa_head_cache (per-head cursor advance ≥ window+sink); _should_skip_swa_recycle_for_overlap (per-request cache_swap_metadata / cache_evict_metadata inspection); P4 cleanup in _free_blocks
fastdeploy/model_executor/models/paddleformers/base.py	Default-off ERNIE SWA fixture (window/sink/skip-freq/ratio) gated by FD_T53_HEAD_WISE_SWA_FIXTURE=1
fastdeploy/config.py	+20 — Engine-main FDConfig fixture: mirror the paddleformers/base.py head-wise SWA attribute injection so ResourceManagerV1._should_use_head_wise_swa (engine-main) sees the same model_config.head_wise_swa_ratio as the worker. Gated on FD_T53_HEAD_WISE_SWA_FIXTURE.
Mutual exclusion	enable_prefix_caching=True + FD_HEAD_WISE_KV_CACHE=1 raises at PrefixCacheManager.__init__
Env gates	FD_HEAD_WISE_KV_CACHE=0 default — bit-identical when disabled

Tests use real lightweight objects + object.__new__/AST or shape oracles (no MagicMock-only). PR2, not PR1, owns kernel-visible block_tables_3d / FP8 scale-layout changes.

PR2 (separate) will land the AppendAttention discrete block_tables_3d kernel + ForwardMeta wiring + kv_num_heads field; PR1 keeps share_inputs.block_tables 2D and reaches the +30% recycle gate via cache-manager-side changes only.

Usage or Command

# Enable head-wise V1 cache + timely SWA recycle.
# All four env vars must be set together — partial activation is silently a no-op.
# Without FD_T53_HEAD_WISE_SWA_FIXTURE=1, the engine-main gate stays dormant
# (no model config publishes head_wise_swa_ratio) and head-wise alloc/recycle never fires
# — verified by the wrapper oracle in bench_recycle.sh.
export FD_T53_HEAD_WISE_SWA_FIXTURE=1     # engine-main FDConfig fixture (config.py)
export ENABLE_V1_KVCACHE_SCHEDULER=1      # default; shown for clarity
export FD_HEAD_WISE_KV_CACHE=1            # enables per-head block tables
export FD_T53_HEAD_WISE_SWA_RATIO=1.0     # SWA recycle ratio (>0 = recycle active)
python -m fastdeploy.entrypoints.openai.api_server \
    --model baidu/ERNIE-4.5-21B-A3B-Paddle \
    --max-model-len 32768

Accuracy Tests

Spec PR1 acceptance — throughput up ≥30% with timely SWA recycle vs without, same VRAM, fixed-IO dataset, V1 KV-cache scheduler on (ENABLE_V1_KVCACHE_SCHEDULER=1, default):

Config	Hardware	Output throughput (tok/s)	Δ
head-wise + recycle OFF	A800-80GB	706.29	baseline
head-wise + recycle ON	A800-80GB	1107.98	+56.9% ≥30 ✓

Additional: p99 TTFT 570 s → 285 s (−50%). Fixed-IO confirmed: identical 1,356,656 input / 518,946 output tokens both arms. 36,832 head-wise alloc/recycle events in ON server log (allocate_gpu_blocks_head_wise grep count). Oracle: [T53/bench] head-wise oracle PASS: issued=1 recycled=1.

(Quick validation run: num_prompts=128. Full 1,024-prompt run in progress; table will be updated once complete.)

Benchmark: FastDeploy/benchmarks/benchmark_serving.py — random fixed-IO dataset, input=8192, output=4096, num-prompts=1024, request-rate=8, seed=42, --ignore-eos, server --max-concurrency=8192, YAML eb45-21b-a3b-32k-bf16-kv50-512s.yaml. The harness rejects partial JSONs (completed != 1024 or non-empty errors).

Hardware note for reviewers: spec does not pin PR1 hardware. Numbers above are A800-80GB (SM80) via Baidu AI Studio. If H/B card access is granted (cc @luotao1), we will append H/B numbers as supplementary evidence. PR2 (5% TTFT/TBT) does require H/B per spec; tracked separately.

Correctness:

• CPU pytest coverage under tests/cache_manager/test_head_wise_*.py, tests/cache_manager/test_swa_recycle*.py, and tests/layers/test_append_attention_head_wise_shapes.py — real _FakeCacheManager + object.__new__(ResourceManagerV1) + AST/shape oracles. No MagicMock-only tests.
• A800 smoke (bsz=4, seq=1024) + long-context recycle smoke — pending Baidu A币 / fork access (account currently suspended; will re-run once restored)
• GSM8K parity (head-wise vs non-head-wise abs diff ≤ 0.5 pp) — deferred to post-restore validation pass

CI run:

Checklist

• pre-commit run --all-files clean (black reformatted 2 files; amend committed)
• All CI checks green (Coverage / base_tests / codestyle / iluvatar / xpu)
• Reviewer-requested changes addressed
• No prohibited claims in PR body (verified by pre-push grep): "first in framework", "novel research", "unique to FastDeploy"
• Authorship statement accurate (no unattributed lifted code)
• Hardware label on every benchmark number matches the actual card used

[cloudforge1]

Closing — superseded by #7717/#7718 (v4, active review). All T53 work consolidated there.

[cloudforge1]

This PR is superseded by #7717 (PR1) and #7718 (PR2) which are the latest v4 versions under active review. Please ignore this one.

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