Phase 87: Inline Slots Overflow Observation - Infrastructure Setup (COMPLETE)

Phase 87-1: Telemetry Box Created ✓

Files Added

core/box/tiny_inline_slots_overflow_stats_box.h
- Global counter structure: TinyInlineSlotsOverflowStats
- Counters: C3/C4/C5/C6 push_full, pop_empty, overflow_to_uc, overflow_to_legacy
- Fast-path inline API with __builtin_expect() for zero-cost when disabled
- Enabled via compile-time gate:
  - HAKMEM_INLINE_SLOTS_OVERFLOW_STATS_COMPILED=0/1 (default 0)
  - Non-RELEASE builds can also enable it (depending on build flags)
core/box/tiny_inline_slots_overflow_stats_box.c
- Global state initialization
- Refresh function placeholder
- Report function for final statistics output

Makefile Integration

Added core/box/tiny_inline_slots_overflow_stats_box.o to:
- OBJS_BASE
- BENCH_HAKMEM_OBJS_BASE
- TINY_BENCH_OBJS_BASE
OBSERVE build enables telemetry explicitly:
- make bench_random_mixed_hakmem_observe adds -DHAKMEM_INLINE_SLOTS_OVERFLOW_STATS_COMPILED=1

Build Status

✓ Successfully compiled (no errors, no warnings in new code) ✓ Binary ready: bench_random_mixed_hakmem

Next: Phase 87-2 - Counter Integration Points

To enable overflow measurement, counters must be injected at:

Free Path (Push FULL)

Location: core/front/tiny_c6_inline_slots.h:37 (c6_inline_push)
Trigger: When ring is FULL, return 0
Counter: tiny_inline_slots_count_push_full(6)
Similar for C3 (core/front/tiny_c3_inline_slots.h), C4, C5

Alloc Path (Pop EMPTY)

Location: core/front/tiny_c6_inline_slots.h:54 (c6_inline_pop)
Trigger: When ring is EMPTY, return NULL
Counter: tiny_inline_slots_count_pop_empty(6)
Similar for C3, C4, C5

Fallback Destinations (Unified Cache)

Location: core/front/tiny_unified_cache.h:177-216 (unified_cache_push)
Trigger: When unified cache is FULL, return 0
Counter: tiny_inline_slots_count_overflow_to_uc()
Also: when unified_cache_push returns 0, legacy path gets called
Counter: tiny_inline_slots_count_overflow_to_legacy()

Testing Plan (Phase 87-2)

Observation Conditions

Profile: MIXED_TINYV3_C7_SAFE
Working Set: WS=400 (default inline slots conditions)
Iterations: 20M (ITERS=20000000)
Runs: single-run OBSERVE preflight (SSOT throughput runs remain Standard/FAST)

Expected Output

Debug build will print statistics:

=== PHASE 87: INLINE SLOTS OVERFLOW STATS ===

PUSH FULL (Free Path Ring Overflow):
  C3: ...
  C4: ...
  C5: ...
  C6: ...

POP EMPTY (Alloc Path Ring Underflow):
  C3: ...
  C4: ...
  C5: ...
  C6: ...

Note: `OVERFLOW DESTINATIONS` counters are optional and may remain 0 unless explicitly instrumented at fallback call sites.

GO/NO-GO Decision Logic

GO for Phase 88 if:

(push_full + pop_empty) / (20M * 3 runs) ≥ 0.1%
Indicates sufficient overflow frequency to warrant batch optimization

NO-GO for Phase 88 if:

Overflow rate < 0.1%
Suggests overhead reduction ROI is minimal
Consider alternative optimization layers

Architecture Notes

Counters use _Atomic for thread-safety (single increment per operation)
Zero overhead in RELEASE builds (compile-time constant folding)
Reporting happens on exit (calls tiny_inline_slots_overflow_report_stats())
Call point: Should add to bench program exit sequence

Files Status

File	Status
tiny_inline_slots_overflow_stats_box.h	✓ Created
tiny_inline_slots_overflow_stats_box.c	✓ Created
Makefile	✓ Updated (object files added)
C3/C4/C5/C6 inline slots	⏳ Pending counter integration
Observation binary build	⏳ Pending debug build

Ready for Phase 87-2

Next action: Inject counters into inline slots and run RUNS=3 observation.

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