4a070d8a14
Target: Consolidate free wrapper TLS reads (2→1)
- free() is 25.26% self% (top hot spot)
- Strategy: Apply E1 success pattern (ENV snapshot) to free path
Implementation:
- ENV gate: HAKMEM_FREE_WRAPPER_ENV_SNAPSHOT=0/1 (default 0)
- core/box/free_wrapper_env_snapshot_box.{h,c}: New box
- Consolidates 2 TLS reads → 1 TLS read (50% reduction)
- Reduces 4 branches → 3 branches (25% reduction)
- Lazy init with probe window (bench_profile putenv sync)
- core/box/hak_wrappers.inc.h: Integration in free() wrapper
- Makefile: Add free_wrapper_env_snapshot_box.o to all targets
A/B Test Results (Mixed, 10-run, 20M iters):
- Baseline (SNAPSHOT=0): 45.35M ops/s (mean), 45.31M ops/s (median)
- Optimized (SNAPSHOT=1): 46.94M ops/s (mean), 47.15M ops/s (median)
- Improvement: +3.51% mean, +4.07% median
Decision: GO (+3.51% >= +1.0% threshold)
- Exceeded conservative estimate (+1.5% → +3.51%)
- Similar efficiency to E1 (+3.92%)
- Health check: PASS (all profiles)
- Action: PROMOTED to MIXED_TINYV3_C7_SAFE preset
Phase 5 Cumulative:
- E1 (ENV Snapshot): +3.92%
- E4-1 (Free Wrapper Snapshot): +3.51%
- Total Phase 4-5: ~+7.5%
E3-4 Correction:
- Phase 4 E3-4 (ENV Constructor Init): NO-GO / FROZEN
- Initial A/B showed +4.75%, but investigation revealed:
- Branch prediction hint mismatch (UNLIKELY with always-true)
- Retest confirmed -1.78% regression
- Root cause: __builtin_expect(..., 0) with ctor_mode==1
- Decision: Freeze as research box (default OFF)
- Learning: Branch hints need careful tuning, TLS consolidation safer
Deliverables:
- docs/analysis/PHASE5_E4_FREE_GATE_OPTIMIZATION_1_DESIGN.md
- docs/analysis/PHASE5_E4_1_FREE_WRAPPER_ENV_SNAPSHOT_NEXT_INSTRUCTIONS.md
- docs/analysis/PHASE5_E4_2_MALLOC_WRAPPER_ENV_SNAPSHOT_NEXT_INSTRUCTIONS.md (next)
- docs/analysis/PHASE5_POST_E1_NEXT_INSTRUCTIONS.md
- docs/analysis/ENV_PROFILE_PRESETS.md (E4-1 added, E3-4 corrected)
- CURRENT_TASK.md (E4-1 complete, E3-4 frozen)
- core/bench_profile.h (E4-1 promoted to default)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
86 lines
3.4 KiB
C
86 lines
3.4 KiB
C
// hakmem_env_snapshot_box.h - Phase 4 E1: ENV Snapshot Consolidation
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//
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// Purpose: Consolidate 3 hot ENV gate calls into 1 TLS snapshot read
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// Target: tiny_c7_ultra_enabled_env (1.28%) + tiny_front_v3_enabled (1.01%) +
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// tiny_metadata_cache_enabled (0.97%) = 3.26% combined ENV overhead
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//
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// Design:
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// - ENV: HAKMEM_ENV_SNAPSHOT=0/1 (default 0, research box)
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// - Single TLS snapshot struct containing all hot toggles
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// - Lazy init with version-based refresh (follows tiny_front_v3_snapshot pattern)
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// - Learner interlock: tiny_metadata_cache_eff = cache && !learner
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//
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// E3-4 Extension: Constructor init to eliminate lazy check overhead
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// - ENV: HAKMEM_ENV_SNAPSHOT_CTOR=0/1 (default 0)
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// - When =1: Gate init runs in constructor (before main)
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// - Eliminates 3.22% lazy init check overhead
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//
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// Benefits:
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// - 3 TLS reads → 1 TLS read (66% reduction)
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// - 3 lazy init checks → 1 lazy init check
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// - E3-4: Lazy init check → no check (constructor init)
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// - Expected gain: +1-3% (E1) + +0.5-1.5% (E3-4)
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#ifndef HAK_ENV_SNAPSHOT_BOX_H
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#define HAK_ENV_SNAPSHOT_BOX_H
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#include <stdbool.h>
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#include <stdlib.h>
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// ENV snapshot struct: consolidates all hot ENV gates
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typedef struct HakmemEnvSnapshot {
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bool tiny_c7_ultra_enabled; // ENV: HAKMEM_TINY_C7_ULTRA (default 1)
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bool tiny_front_v3_enabled; // ENV: HAKMEM_TINY_FRONT_V3_ENABLED (default 1)
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bool tiny_metadata_cache; // ENV: HAKMEM_TINY_METADATA_CACHE (default 0)
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bool tiny_metadata_cache_eff; // Effective: cache && !learner (for hot path)
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} HakmemEnvSnapshot;
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// Global snapshot state (implemented in hakmem_env_snapshot_box.c)
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extern HakmemEnvSnapshot g_hakmem_env_snapshot;
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extern int g_hakmem_env_snapshot_ready;
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// Snapshot initializer (implemented in hakmem_env_snapshot_box.c)
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void hakmem_env_snapshot_init(void);
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// Refresh from ENV (for bench_profile putenv sync)
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void hakmem_env_snapshot_refresh_from_env(void);
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// Fast snapshot getter: lazy init + 1 TLS read
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static inline const HakmemEnvSnapshot* hakmem_env_snapshot(void) {
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if (__builtin_expect(!g_hakmem_env_snapshot_ready, 0)) {
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hakmem_env_snapshot_init();
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}
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return &g_hakmem_env_snapshot;
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}
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// E3-4: Global gate state (defined in hakmem_env_snapshot_box.c)
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extern int g_hakmem_env_snapshot_gate;
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extern int g_hakmem_env_snapshot_ctor_mode;
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// ENV gate: default OFF (research box, set =1 to enable)
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// E3-4: Dual-mode - constructor init (fast) or legacy lazy init (fallback)
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static inline bool hakmem_env_snapshot_enabled(void) {
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// E3-4 Fast path: constructor mode (no lazy check, just global read).
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// Important: do not put a static LIKELY/UNLIKELY hint here.
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// - Default runs want ctor_mode==0 to be "fast"
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// - CTOR runs want ctor_mode==1 to be "fast"
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// Any fixed hint will be wrong for one of the modes and can induce steady-state mispredicts.
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int ctor_mode = g_hakmem_env_snapshot_ctor_mode;
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if (ctor_mode == 1) {
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return g_hakmem_env_snapshot_gate != 0;
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}
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// Legacy path: lazy init (fallback when HAKMEM_ENV_SNAPSHOT_CTOR=0)
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if (__builtin_expect(g_hakmem_env_snapshot_gate == -1, 0)) {
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const char* e = getenv("HAKMEM_ENV_SNAPSHOT");
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if (e && *e) {
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g_hakmem_env_snapshot_gate = (*e == '1') ? 1 : 0;
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} else {
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g_hakmem_env_snapshot_gate = 0; // default: OFF (research box)
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}
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}
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return g_hakmem_env_snapshot_gate != 0;
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}
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#endif // HAK_ENV_SNAPSHOT_BOX_H
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