Phase 30-31: Standard procedure + g_tiny_free_trace atomic prune
Phase 30: Standard Procedure Establishment - Created 4-step standardized methodology (Step 0-3) - Step 0: Execution Verification (NEW - Phase 29 lesson) - Step 1: CORRECTNESS/TELEMETRY Classification (Phase 28 lesson) - Step 2: Compile-Out Implementation (Phase 24-27 pattern) - Step 3: A/B Test (build-level comparison) - Executed audit_atomics.sh: 412 atomics analyzed - Identified Phase 31 candidate: g_tiny_free_trace (HOT path, TOP PRIORITY) Phase 31: g_tiny_free_trace Compile-Out (HOT Path TELEMETRY) - Target: core/hakmem_tiny_free.inc:326 (trace-rate-limit atomic) - Added HAKMEM_TINY_FREE_TRACE_COMPILED (default: 0) - Classification: Pure TELEMETRY (trace output only, no flow control) - A/B Result: NEUTRAL (baseline -0.35% mean, +0.19% median) - Verdict: NEUTRAL → Adopted for code cleanliness (Phase 26 precedent) - Rationale: HOT path TELEMETRY removal improves code quality A/B Test Details: - Baseline (COMPILED=0): 53.638M ops/s mean, 53.799M median - Compiled-in (COMPILED=1): 53.828M ops/s mean, 53.697M median - Conflicting signals within ±0.5% noise margin - Phase 25 comparison: g_free_ss_enter (+1.07% GO) vs g_tiny_free_trace (NEUTRAL) - Hypothesis: Rate-limited atomic (128 calls) optimized by compiler Cumulative Progress (Phase 24-31): - Phase 24 (class stats): +0.93% GO - Phase 25 (free stats): +1.07% GO - Phase 26 (diagnostics): -0.33% NEUTRAL - Phase 27 (unified cache): +0.74% GO - Phase 28 (bg spill): NO-OP (all CORRECTNESS) - Phase 29 (pool v2): NO-OP (ENV-gated) - Phase 30 (procedure): PROCEDURE - Phase 31 (free trace): -0.35% NEUTRAL - Total: 18 atomics removed, +2.74% net improvement Documentation Created: - PHASE30_STANDARD_PROCEDURE.md: Complete 4-step methodology - ATOMIC_AUDIT_FULL.txt: 412 atomics comprehensive audit - PHASE31_CANDIDATES_HOT/WARM.txt: Priority-sorted candidates - PHASE31_RECOMMENDED_CANDIDATES.md: TOP 3 with Step 0 verification - PHASE31_TINY_FREE_TRACE_ATOMIC_PRUNE_RESULTS.md: Complete A/B results - ATOMIC_PRUNE_CUMULATIVE_SUMMARY.md: Updated (Phase 30-31) - CURRENT_TASK.md: Phase 32 candidate identified (g_hak_tiny_free_calls) Key Lessons: - Lesson 7 (Phase 30): Step 0 execution verification prevents wasted effort - Lesson 8 (Phase 31): NEUTRAL + code cleanliness = valid adoption - HOT path ≠ guaranteed performance win (rate-limited atomics may be optimized) Next Phase: Phase 32 candidate (g_hak_tiny_free_calls) - Location: core/hakmem_tiny_free.inc:335 (9 lines below Phase 31 target) - Expected: +0.3~0.7% or NEUTRAL Generated with Claude Code https://claude.com/claude-code Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
This commit is contained in:
Moe Charm (CI)
@ -3,7 +3,7 @@
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**Project:** HAKMEM Memory Allocator - Hot Path Optimization
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**Goal:** Remove all telemetry-only atomics from hot alloc/free paths
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**Principle:** Follow mimalloc: No atomics/observe in hot path
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**Status:** Phase 24+25+26+27 Complete (+2.74% cumulative), Phase 28 Audit Complete (NO-OP)
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**Status:** Phase 24+25+26+27+31 Complete (+2.74% cumulative), Phase 28+29 NO-OP, Phase 30 Procedure Complete
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---
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@ -203,6 +203,83 @@ rg "getenv.*FEATURE" && echo "⚠️ ENV-gated, may be OFF"
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---
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### Phase 30: Standard Procedure Documentation ✅ **PROCEDURE COMPLETE**
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**Date:** 2025-12-16
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**Target:** Standardization of atomic prune methodology (not a performance phase)
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**Purpose:** Codify learnings from Phase 24-29 into reusable 4-step procedure
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**Deliverables:**
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1. `docs/analysis/PHASE30_STANDARD_PROCEDURE.md` - 4-step standardized methodology
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2. `docs/analysis/ATOMIC_AUDIT_FULL.txt` - Complete atomic audit (412 atomics)
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3. `docs/analysis/PHASE31_RECOMMENDED_CANDIDATES.md` - Phase 31 candidate selection
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**4-Step Standard Procedure:**
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**Step 0: Execution Verification (NEW - Phase 29 lesson)**
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- Check for ENV gates (`getenv()` checks)
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- Verify execution counters > 0 in benchmark
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- Use perf/flamegraph to confirm code path is hit
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- **Decision:** SKIP if ENV-gated or not executed
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**Step 1: CORRECTNESS/TELEMETRY Classification (Phase 28 lesson)**
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- Track all atomic usage sites
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- Check for `if` conditions (CORRECTNESS)
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- Verify pure telemetry usage (TELEMETRY)
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- **Decision:** DO NOT TOUCH if CORRECTNESS
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**Step 2: Compile-Out Implementation (Phase 24-27 pattern)**
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- Add `HAKMEM_*_COMPILED` flag to `hakmem_build_flags.h`
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- Wrap atomics with `#if` preprocessor gates
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- Build-level compile-out (not link-out)
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**Step 3: A/B Test (build-level comparison)**
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- Baseline (COMPILED=0): default build
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- Compiled-in (COMPILED=1): research build
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- Compare 10-run averages
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- **Verdict:** GO (+0.5%+), NEUTRAL (±0.5%), NO-GO (-0.5%+)
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**Audit Results (Phase 30):**
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- **Total atomics:** 412 (104 TELEMETRY, 24 CORRECTNESS, 284 UNKNOWN)
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- **HOT path:** 16 atomics (5 TELEMETRY, 11 UNKNOWN)
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- **WARM path:** 10 atomics (3 TELEMETRY, 7 UNKNOWN)
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- **COLD path:** 386 atomics (remaining)
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**Phase 31 Candidate Selection:**
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- **TOP PRIORITY:** `g_tiny_free_trace` (HOT path, TELEMETRY, execution verified)
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- **Expected Impact:** +0.5% to +1.0% (similar to Phase 25)
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- **Skipped:** 2 ENV-gated WARM path candidates (Phase 29 lesson applied)
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**Key Lesson:** Step 0 (execution verification) prevents wasted effort on ENV-gated or inactive code paths. Phase 29 taught us that optimization without execution = zero impact.
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**Reference:** `docs/analysis/PHASE30_STANDARD_PROCEDURE.md`, `docs/analysis/PHASE31_RECOMMENDED_CANDIDATES.md`
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---
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### Phase 31: Tiny Free Trace Atomic Prune ✅ **NEUTRAL (-0.35%)**
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**Date:** 2025-12-16
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**Target:** `g_tiny_free_trace` (tiny free trace rate-limit counter)
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**File:** `core/hakmem_tiny_free.inc:326`
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**Atomics:** 1 global counter (executed on every tiny free)
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**Build Flag:** `HAKMEM_TINY_FREE_TRACE_COMPILED` (default: 0)
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**Results:**
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- **Baseline (compiled-out):** 53.64 M ops/s (mean), 53.80 M ops/s (median)
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- **Compiled-in:** 53.83 M ops/s (mean), 53.70 M ops/s (median)
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- **Improvement:** **-0.35% (mean), +0.19% (median)**
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- **Verdict:** **NEUTRAL** ➡️ Keep compiled-out for cleanliness ✅
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**Analysis:** HOT path atomic (every free call entry) shows no measurable impact (-0.35% mean, +0.19% median, both within ±0.5% noise margin). Unlike Phase 25 (`g_free_ss_enter`: +1.07%), this trace rate-limit atomic (128 calls) does not show performance overhead. Following Phase 26 precedent (-0.33% NEUTRAL, adopted for cleanliness), Phase 31 is ADOPTED with COMPILED=0 as default.
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**Path:** HOT (entry point of `hak_tiny_free()`)
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**Frequency:** High (every tiny free call, but rate-limited to 128 traces)
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**Key Finding:** Not all HOT path atomics have measurable overhead. Rate-limited trace may be optimized by compiler.
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**Reference:** `docs/analysis/PHASE31_TINY_FREE_TRACE_ATOMIC_PRUNE_RESULTS.md`
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---
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## Cumulative Impact
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| Phase | Atomics Removed | Frequency | Impact | Status |
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| 27 | 6 (unified cache) | Medium (refills) | **+0.74%** | GO ✅ |
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| **28** | **0 (bg spill)** | **N/A (all CORRECTNESS)** | **N/A** | **NO-OP ✅** |
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| **29** | **0 (pool v2)** | **N/A (code not active)** | **0.00%** | **NO-OP ✅** |
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| **Total** | **17 atomics** | **Mixed** | **+2.74%** | **✅** |
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| **30** | **0 (procedure)** | **N/A (standardization)** | **N/A** | **PROCEDURE ✅** |
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| **31** | **1 (free trace)** | **High (every free entry)** | **-0.35%** | **NEUTRAL ✅** |
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| **Total** | **18 atomics** | **Mixed** | **+2.74%** | **✅** |
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**Key Insights:**
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1. **Frequency matters more than count:** High-frequency atomics (Phase 24+25) provide measurable benefit (+0.93%, +1.07%). Medium-frequency atomics (Phase 27, WARM path) provide substantial benefit (+0.74%). Low-frequency atomics (Phase 26) provide cleanliness but no performance gain.
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2. **Correctness atomics are untouchable:** Phase 28 showed that lock-free queues and flow control counters must not be touched.
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3. **ENV-gated code paths need verification:** Phase 29 showed that compile-out of inactive code has zero performance impact. Always verify code is active before A/B testing.
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4. **Standardized procedure prevents wasted effort:** Phase 30 codified 4-step procedure with Step 0 (execution verification) as mandatory gate to avoid Phase 29-style no-ops.
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5. **HOT path ≠ guaranteed performance win:** Phase 31 showed that even HOT path atomics may have zero measurable overhead if rate-limited or well-optimized. NEUTRAL results still justify adoption for code cleanliness (Phase 26/31 precedent).
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---
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## Lessons Learned
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### 1. Frequency Trumps Count
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### 1. Frequency Trumps Count (But Not Always)
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- **Phase 24:** 5 atomics, high frequency → +0.93% ✅
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- **Phase 25:** 1 atomic, high frequency → +1.07% ✅
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- **Phase 26:** 5 atomics, low frequency → -0.33% (NEUTRAL)
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- **Phase 31:** 1 atomic, high frequency → -0.35% (NEUTRAL)
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**Takeaway:** Focus on always-executed atomics, not just atomic count.
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**Takeaway:** Focus on always-executed atomics, not just atomic count. However, even high-frequency atomics may have zero measurable overhead if optimized (e.g., rate-limited, compiler optimization).
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### 2. Edge Cases Don't Matter (Performance-Wise)
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- Phase 26 atomics are in error/diagnostic paths (header mismatch, bad class, etc.)
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@ -262,9 +344,22 @@ rg "getenv.*FEATURE" && echo "⚠️ ENV-gated, may be OFF"
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3. Or use `perf record` to check if functions are called
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- **Anomaly:** Compiled-in was 0.62% faster (noise due to compiler artifacts, not real effect)
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### 7. Standard Procedure is Reusable (NEW: Phase 30)
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- **Phase 30:** Codified 4-step procedure from Phase 24-29 learnings
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- **Step 0 (execution verification):** Prevents Phase 29-style wasted effort on ENV-gated code
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- **Step 1 (classification):** Prevents Phase 28-style mistakes (CORRECTNESS vs TELEMETRY)
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- **Step 2-3 (implementation + A/B test):** Proven pattern from Phase 24-27
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- **Result:** Systematic atomic audit (412 atomics), Phase 31 candidate selected with high confidence
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### 8. NEUTRAL + Cleanliness = Valid Adoption (Phase 26/31 Pattern)
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- **Phase 26:** -0.33% NEUTRAL → Adopted for code cleanliness
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- **Phase 31:** -0.35% NEUTRAL → Adopted for code cleanliness (same precedent)
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- **Rationale:** No performance regression (within noise), reduces complexity, maintains research flexibility (COMPILED=1 available)
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- **Takeaway:** NEUTRAL verdicts justify compile-out even without performance wins
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---
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## Next Phase Candidates (Phase 30+)
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## Next Phase Candidates (Phase 31+)
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### Completed Audits
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@ -276,9 +371,38 @@ rg "getenv.*FEATURE" && echo "⚠️ ENV-gated, may be OFF"
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- **Result:** All TELEMETRY atomics, but code path not active (ENV-gated)
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- **Reason:** `HAKMEM_POOL_V2_ENABLED` defaults to OFF
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### High Priority: Warm Path Atomics
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3. ~~**Standard Procedure Documentation** (Phase 30)~~ ✅ **COMPLETE (PROCEDURE)**
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- **Result:** 4-step procedure standardized, atomic audit complete (412 atomics)
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- **Reason:** Methodology standardization, not a performance phase
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3. **Remote Target Queue** (Phase 30 candidate)
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### High Priority: Phase 32 Target (NEXT)
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4. ~~**Tiny Free Trace Atomic** (Phase 31)~~ ✅ **COMPLETE (NEUTRAL -0.35%)**
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- **Result:** NEUTRAL verdict, adopted for code cleanliness
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- **Reason:** HOT path atomic with zero measurable overhead (rate-limited trace)
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5. **Tiny Free Calls Counter** (Phase 32 - TOP PRIORITY) ⭐
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- **Target:** `g_hak_tiny_free_calls` (HOT path)
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- **File:** `core/hakmem_tiny_free.inc:335` (9 lines after Phase 31 target)
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- **Atomic:** 1 counter (`atomic_fetch_add`)
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- **Classification:** TELEMETRY ✅ (diagnostic counter only)
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- **Execution:** ✅ Verified (same function as Phase 31, no ENV gate)
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- **Frequency:** HOT (every tiny free call, same as Phase 31)
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- **Expected Gain:** +0.3% to +0.7% (smaller than Phase 25, similar to Phase 31)
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- **Priority:** **HIGHEST** (same HOT path as Phase 31)
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- **Reference:** `docs/analysis/PHASE31_TINY_FREE_TRACE_ATOMIC_PRUNE_RESULTS.md` (Phase 32 candidate)
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### Medium Priority: Uncertain Candidates
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6. **P0 Class OOB Log** (Phase 33 candidate)
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- **Target:** `g_p0_class_oob_log` (WARM path)
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- **File:** `core/hakmem_tiny_refill_p0.inc.h:41`
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- **Classification:** TELEMETRY (error logging)
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- **Execution:** ❓ UNCERTAIN (error path, needs verification)
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- **Expected Gain:** ±0.0% to +0.2%
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- **Priority:** MEDIUM (verify execution first)
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7. **Remote Target Queue** (Phase 34 candidate)
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- **Targets:** `g_remote_target_len[class_idx]` atomics
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- **File:** `core/hakmem_tiny_remote_target.c`
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- **Atomics:** `atomic_fetch_add/sub` on queue length
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- **Priority:** MEDIUM (needs correctness review - similar to bg_spill)
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- **Warning:** May be flow control like `g_bg_spill_len`, needs audit
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### Low Priority: ENV-gated (SKIP)
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8. ~~**Warm Pool Prefill Logs** (SKIP - ENV-gated)~~
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- **Targets:** `rel_logs`, `dbg_logs` (WARM path)
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- **Files:** `core/box/warm_pool_prefill_box.h`, `core/hakmem_tiny_refill.inc.h`
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- **Classification:** TELEMETRY (fprintf only)
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- **Execution:** ❌ ENV-gated (HAKMEM_TINY_WARM_LOG=OFF by default)
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- **Expected Gain:** 0.0% (NO-OP, Phase 29 lesson)
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- **Priority:** SKIP (not executed in benchmark)
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### Low Priority: Cold Path Atomics
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4. **SuperSlab OS Stats** (Phase 30+)
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9. **SuperSlab OS Stats** (Phase 35+)
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- **Targets:** `g_ss_os_alloc_calls`, `g_ss_os_madvise_calls`, etc.
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- **Files:** `core/box/ss_os_acquire_box.h`, `core/box/madvise_guard_box.c`
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- **Frequency:** Cold (init/mmap/madvise)
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- **Expected Gain:** <0.1%
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- **Priority:** LOW (code cleanliness only)
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5. **Shared Pool Diagnostics** (Phase 31+)
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- **Targets:** `rel_c7_*`, `dbg_c7_*` (release/acquire logs)
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- **Files:** `core/hakmem_shared_pool_acquire.c`, `core/hakmem_shared_pool_release.c`
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- **Frequency:** Cold (shared pool operations)
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- **Expected Gain:** <0.1%
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- **Priority:** LOW
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---
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## Pattern Template (For Future Phases)
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@ -406,6 +533,11 @@ All atomic compile gates in `core/hakmem_build_flags.h`:
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#ifndef HAKMEM_POOL_HOTBOX_V2_STATS_COMPILED
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# define HAKMEM_POOL_HOTBOX_V2_STATS_COMPILED 0
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#endif
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// Phase 31: Tiny Free Trace (NEUTRAL -0.35%)
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#ifndef HAKMEM_TINY_FREE_TRACE_COMPILED
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# define HAKMEM_TINY_FREE_TRACE_COMPILED 0
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#endif
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```
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**Default State:** All flags = 0 (compiled-out, production-ready)
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@ -415,12 +547,13 @@ All atomic compile gates in `core/hakmem_build_flags.h`:
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## Conclusion
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**Total Progress (Phase 24+25+26+27+28+29):**
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- **Performance Gain:** +2.74% (Phase 24: +0.93%, Phase 25: +1.07%, Phase 26: NEUTRAL, Phase 27: +0.74%, Phase 28: NO-OP, Phase 29: NO-OP)
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- **Atomics Removed:** 17 telemetry atomics from hot/warm paths
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- **Phases Completed:** 6 phases (4 with changes, 2 audit-only)
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**Total Progress (Phase 24+25+26+27+28+29+30+31):**
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- **Performance Gain:** +2.74% (Phase 24: +0.93%, Phase 25: +1.07%, Phase 26: NEUTRAL, Phase 27: +0.74%, Phase 28: NO-OP, Phase 29: NO-OP, Phase 30: PROCEDURE, Phase 31: NEUTRAL)
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- **Atomics Removed:** 18 telemetry atomics from hot/warm paths (17 compiled-out + 1 Phase 31)
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- **Phases Completed:** 8 phases (4 with performance changes, 2 audit-only, 1 standardization, 1 cleanliness)
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- **Code Quality:** Cleaner hot/warm paths, closer to mimalloc's zero-overhead principle
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- **Next Target:** Phase 30 (remote target queue or other ACTIVE code paths)
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- **Methodology:** 4-step standard procedure validated (Phase 30-31)
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- **Next Target:** Phase 32 (`g_hak_tiny_free_calls`, HOT path, expected +0.3% to +0.7%)
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**Key Success Factors:**
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1. Systematic audit and classification (CORRECTNESS vs TELEMETRY)
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@ -428,21 +561,28 @@ All atomic compile gates in `core/hakmem_build_flags.h`:
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3. Clear verdict criteria (GO/NEUTRAL/NO-GO)
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4. Focus on high-frequency atomics for performance
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5. Compile-out low-frequency atomics for cleanliness
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6. **NEW:** Step 0 execution verification (Phase 30 standard procedure)
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**Future Work:**
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- Continue Phase 29+ (warm/cold path atomics)
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- Expected cumulative gain: +3.0-3.5% total (already at +2.74%)
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- Focus on high-frequency paths, audit carefully for CORRECTNESS vs TELEMETRY
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- **Immediate:** Phase 32 (`g_hak_tiny_free_calls`, HOT path, same location as Phase 31)
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- Expected cumulative gain: +3.0-3.5% total (currently at +2.74%)
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- Follow Phase 30 standard procedure for all future candidates
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- Focus on execution-verified, high-frequency paths
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- Document all verdicts for reproducibility
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- Accept NEUTRAL verdicts for code cleanliness (Phase 26/31 pattern)
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**Lessons from Phase 28+29:**
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**Lessons from Phase 28+29+30+31:**
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- Not all atomic counters are telemetry (Phase 28: flow control counters are CORRECTNESS)
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- Flow control counters (e.g., `g_bg_spill_len`) are UNTOUCHABLE
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- Always trace how counter is used before classifying
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- Verify code path is ACTIVE before A/B testing (Phase 29: ENV-gated code has zero impact)
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- Standard procedure prevents repeated mistakes (Phase 30: Step 0 gate prevents Phase 29-style no-ops)
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- Not all HOT path atomics have measurable overhead (Phase 31: -0.35% NEUTRAL despite high frequency)
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- NEUTRAL verdicts justify adoption for code cleanliness (Phase 26/31 precedent)
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---
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**Last Updated:** 2025-12-16
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**Status:** Phase 24+25+26+27 Complete (+2.74%), Phase 28+29 Audit Complete (NO-OP x2)
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**Status:** Phase 24-27+31 Complete (+2.74%), Phase 28-29 NO-OP, Phase 30 Procedure Complete
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**Next Phase:** Phase 32 (`g_hak_tiny_free_calls`, HOT path, expected +0.3% to +0.7%)
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||||
**Maintained By:** Claude Sonnet 4.5
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620
docs/analysis/PHASE30_STANDARD_PROCEDURE.md
Normal file
620
docs/analysis/PHASE30_STANDARD_PROCEDURE.md
Normal file
@ -0,0 +1,620 @@
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# Phase 30: Standard Procedure for Atomic Prune Operations
|
||||
|
||||
**Date:** 2025-12-16
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||||
**Status:** PROCEDURE STANDARDIZATION
|
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**Purpose:** Codify learnings from Phase 24-29 to prevent no-op phases
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|
||||
---
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||||
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||||
## Executive Summary
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||||
|
||||
Phase 24-29 taught us critical lessons about atomic pruning success factors:
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- **GO phases** (+2.74% cumulative): HOT/WARM path telemetry atomic removal works
|
||||
- **NO-OP phases** (Phase 28-29): Correctness atomics and ENV-gated code waste effort
|
||||
|
||||
This document standardizes a 4-step procedure to ensure future phases target high-impact, executable code.
|
||||
|
||||
---
|
||||
|
||||
## 1. Phase 24-29 Cumulative Lessons
|
||||
|
||||
### Phase 24-27: GO (+2.74% cumulative)
|
||||
|
||||
**Pattern: HOT/WARM path telemetry atomic removal**
|
||||
|
||||
- **Phase 24 (alloc stats)**: +0.93%
|
||||
- Removed `atomic_fetch_add` in `malloc_tiny_fast()` hot path
|
||||
- Stats compiled out with `HAKMEM_ALLOC_GATE_STATS_COMPILED=0`
|
||||
|
||||
- **Phase 25 (free stats)**: +1.07%
|
||||
- Removed `atomic_fetch_add` in `free_tiny_fast_hotcold()` hot path
|
||||
- Stats compiled out with `HAKMEM_FREE_PATH_STATS_COMPILED=0`
|
||||
|
||||
- **Phase 27 (unified cache)**: +0.74%
|
||||
- Removed `atomic_fetch_add` in TLS cache hit path
|
||||
- Stats compiled out with `HAKMEM_TINY_FRONT_STATS_COMPILED=0`
|
||||
|
||||
**Success Factors:**
|
||||
- ✅ Executed in every allocation/free (HOT path)
|
||||
- ✅ Pure telemetry (stats only, no control flow)
|
||||
- ✅ Build-level compile-out (no runtime overhead)
|
||||
|
||||
### Phase 26: NEUTRAL (code cleanliness)
|
||||
|
||||
**Pattern: Low-frequency but still compile-out**
|
||||
|
||||
- Tiny header tracking stats (COLD path)
|
||||
- No performance impact but maintains future maintainability
|
||||
- Kept compile-out mechanism for consistency
|
||||
|
||||
**Lesson:** Even low-frequency telemetry benefits from compile-out for code cleanliness.
|
||||
|
||||
### Phase 28: NO-OP (CORRECTNESS atomics)
|
||||
|
||||
**Anti-pattern: Misidentified counter purpose**
|
||||
|
||||
- **Target:** `g_bg_spill_len` (looked like a counter)
|
||||
- **Reality:** Flow control atomic (queue depth tracking)
|
||||
- **Usage:**
|
||||
```c
|
||||
if (atomic_load(&g_bg_spill_len) < TARGET_SPILL_LEN) {
|
||||
// Decision-making logic
|
||||
}
|
||||
```
|
||||
|
||||
**Critical Lesson:**
|
||||
**Counter name ≠ Counter purpose**
|
||||
|
||||
**CORRECTNESS atomics (NEVER touch):**
|
||||
- Used in `if/while` conditions
|
||||
- Flow control (queue depth, threshold checks)
|
||||
- Lock-free synchronization (CAS, load-store ordering)
|
||||
- Affects program behavior if removed
|
||||
|
||||
### Phase 29: NO-OP (ENV-gated, not executed)
|
||||
|
||||
**Anti-pattern: Optimizing dead code**
|
||||
|
||||
- **Target:** Pool v2 stats atomics
|
||||
- **Reality:** Gated by `getenv("HAKMEM_POOL_V2")` = OFF by default
|
||||
- **Benchmark:** Never executes pool v2 code paths
|
||||
- **Result:** Zero impact on measurements
|
||||
|
||||
**Critical Lesson:**
|
||||
**Execution verification is MANDATORY before optimization**
|
||||
|
||||
---
|
||||
|
||||
## 2. Standard Procedure (4 Steps)
|
||||
|
||||
### Step 0: Execution Verification (MANDATORY GATE) ⚠️
|
||||
|
||||
**Purpose:** Prevent wasted effort on ENV-gated or low-frequency code (Phase 29 lesson)
|
||||
|
||||
#### Methods:
|
||||
|
||||
**A. ENV Gate Check**
|
||||
```bash
|
||||
# Check if feature is runtime-disabled
|
||||
rg "getenv.*FEATURE_NAME" core/
|
||||
rg "getenv.*POOL_V2" core/ # Example
|
||||
```
|
||||
|
||||
**B. Execution Counter Verification**
|
||||
|
||||
1. **Find counter reference:**
|
||||
```bash
|
||||
rg -n "atomic.*g_target_counter" core/
|
||||
```
|
||||
|
||||
2. **Check counter in benchmark output:**
|
||||
```bash
|
||||
# Run mixed benchmark 10 times
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
|
||||
# Check if counter > 0 in any run
|
||||
grep "target_counter" results/*.txt
|
||||
```
|
||||
|
||||
3. **Optional: Add debug printf (if counter not visible):**
|
||||
```c
|
||||
#if HAKMEM_DEBUG_PRINT
|
||||
fprintf(stderr, "[DEBUG] counter=%lu\n",
|
||||
atomic_load(&g_target_counter));
|
||||
#endif
|
||||
```
|
||||
|
||||
**C. perf/flamegraph Verification (optional but recommended)**
|
||||
```bash
|
||||
# Record with perf
|
||||
perf record -g -F 99 -- ./bench_random_mixed_hakmem
|
||||
|
||||
# Check if function appears in profile
|
||||
perf report | grep "target_function"
|
||||
```
|
||||
|
||||
#### Decision Matrix:
|
||||
|
||||
| Condition | Action |
|
||||
|-----------|--------|
|
||||
| ✅ Counter > 0 in benchmark | Proceed to Step 1 |
|
||||
| ✅ Function in perf profile | Proceed to Step 1 |
|
||||
| ❌ ENV gated + OFF by default | **SKIP** (Phase 29 pattern) |
|
||||
| ❌ Counter = 0 in all runs | **SKIP** (not executed) |
|
||||
| ❌ Function not in flamegraph | **SKIP** (negligible frequency) |
|
||||
|
||||
**Output:** Document execution verification results in `PHASE[N]_AUDIT.md`
|
||||
|
||||
---
|
||||
|
||||
### Step 1: CORRECTNESS/TELEMETRY Classification (Phase 28 lesson)
|
||||
|
||||
**Purpose:** Distinguish between atomics that control behavior vs. atomics that just observe
|
||||
|
||||
#### Classification Rules:
|
||||
|
||||
**CORRECTNESS (NEVER touch):**
|
||||
- ❌ Used in `if/while/for` conditions
|
||||
- ❌ Flow control (queue depth, threshold, capacity checks)
|
||||
- ❌ Lock-free synchronization (CAS, `atomic_compare_exchange_*`)
|
||||
- ❌ Load-store ordering dependencies
|
||||
- ❌ Affects program decisions/behavior
|
||||
|
||||
**Examples:**
|
||||
```c
|
||||
// CORRECTNESS: Controls loop behavior
|
||||
while (atomic_load(&g_queue_len) < target) { ... }
|
||||
|
||||
// CORRECTNESS: Threshold check
|
||||
if (atomic_load(&g_bg_spill_len) >= MAX_SPILL) { ... }
|
||||
|
||||
// CORRECTNESS: CAS synchronization
|
||||
atomic_compare_exchange_weak(&g_state, &expected, desired)
|
||||
```
|
||||
|
||||
**TELEMETRY (compile-out candidate):**
|
||||
- ✅ Stats/logging/observation only
|
||||
- ✅ Used exclusively in `printf/fprintf/sprintf`
|
||||
- ✅ Deletion changes no program behavior
|
||||
- ✅ Pure counters (hits, misses, totals)
|
||||
|
||||
**Examples:**
|
||||
```c
|
||||
// TELEMETRY: Stats only
|
||||
atomic_fetch_add(&stats[idx].hits, 1, memory_order_relaxed);
|
||||
|
||||
// TELEMETRY: Logging only
|
||||
fprintf(stderr, "allocs=%lu\n", atomic_load(&g_alloc_count));
|
||||
```
|
||||
|
||||
#### Verification Process:
|
||||
|
||||
1. **List all atomics in target scope:**
|
||||
```bash
|
||||
rg -n "atomic_(fetch_add|load|store).*g_target" core/
|
||||
```
|
||||
|
||||
2. **Track all usage sites:**
|
||||
```bash
|
||||
rg -n "g_target_atomic" core/
|
||||
```
|
||||
|
||||
3. **Check each usage:**
|
||||
- Is it in an `if` condition? → **CORRECTNESS**
|
||||
- Is it only in `printf/fprintf`? → **TELEMETRY**
|
||||
- Unsure? → **CORRECTNESS** (safe default)
|
||||
|
||||
4. **Document classification:**
|
||||
```markdown
|
||||
## Atomic Classification
|
||||
|
||||
### g_alloc_stats (TELEMETRY)
|
||||
- core/box/alloc_gate_stats_box.h:15: atomic_fetch_add (stats only)
|
||||
- core/hakmem.c:89: fprintf output only
|
||||
- **Verdict:** TELEMETRY ✅
|
||||
|
||||
### g_bg_spill_len (CORRECTNESS)
|
||||
- core/box/bgthread_box.h:42: if (atomic_load(...) < TARGET)
|
||||
- **Verdict:** CORRECTNESS ❌ DO NOT TOUCH
|
||||
```
|
||||
|
||||
**Output:** Classification table in `PHASE[N]_AUDIT.md`
|
||||
|
||||
---
|
||||
|
||||
### Step 2: Compile-Out Implementation (Phase 24-27 pattern)
|
||||
|
||||
**Purpose:** Build-level removal of telemetry atomics (not link-out)
|
||||
|
||||
#### A. Add Compile Gate to BuildFlags
|
||||
|
||||
**File:** `core/hakmem_build_flags.h`
|
||||
|
||||
```c
|
||||
// ========== [Feature Name] Stats (Phase N) ==========
|
||||
#ifndef HAKMEM_[NAME]_STATS_COMPILED
|
||||
# define HAKMEM_[NAME]_STATS_COMPILED 0
|
||||
#endif
|
||||
```
|
||||
|
||||
**Example:**
|
||||
```c
|
||||
// ========== Alloc Gate Stats (Phase 24) ==========
|
||||
#ifndef HAKMEM_ALLOC_GATE_STATS_COMPILED
|
||||
# define HAKMEM_ALLOC_GATE_STATS_COMPILED 0
|
||||
#endif
|
||||
```
|
||||
|
||||
#### B. Wrap TELEMETRY Atomics with #if
|
||||
|
||||
**Pattern:**
|
||||
```c
|
||||
#if HAKMEM_[NAME]_STATS_COMPILED
|
||||
atomic_fetch_add_explicit(&g_[name]_stat, 1, memory_order_relaxed);
|
||||
#else
|
||||
(void)0; // No-op when compiled out
|
||||
#endif
|
||||
```
|
||||
|
||||
**Example:**
|
||||
```c
|
||||
#if HAKMEM_ALLOC_GATE_STATS_COMPILED
|
||||
atomic_fetch_add_explicit(&g_alloc_gate_slow, 1, memory_order_relaxed);
|
||||
#else
|
||||
(void)0;
|
||||
#endif
|
||||
```
|
||||
|
||||
#### C. Keep Variable Definitions (important!)
|
||||
|
||||
**Do NOT remove:**
|
||||
```c
|
||||
// Keep atomic variable definition (for COMPILED=1 case)
|
||||
static _Atomic uint64_t g_stat_counter = 0;
|
||||
|
||||
// Keep print functions (guarded by same flag)
|
||||
#if HAKMEM_[NAME]_STATS_COMPILED
|
||||
void print_stats(void) {
|
||||
fprintf(stderr, "counter=%lu\n", atomic_load(&g_stat_counter));
|
||||
}
|
||||
#endif
|
||||
```
|
||||
|
||||
#### D. Prohibited Actions (Phase 22-2 NO-GO lesson)
|
||||
|
||||
**NEVER:**
|
||||
- ❌ Link-out (removing `.o` files from Makefile)
|
||||
- ❌ Deleting API functions (breaks linkage)
|
||||
- ❌ Removing struct definitions (breaks compilation)
|
||||
- ❌ Runtime `if` checks (adds branch overhead)
|
||||
|
||||
**Rationale:** Build-level `#if` has zero runtime cost. Link-out risks ABI breaks.
|
||||
|
||||
---
|
||||
|
||||
### Step 3: A/B Test (build-level comparison)
|
||||
|
||||
**Purpose:** Measure impact of compile-out vs. compiled-in
|
||||
|
||||
#### A. Baseline Build (COMPILED=0, default)
|
||||
|
||||
```bash
|
||||
# Clean build with stats compiled OUT
|
||||
make clean
|
||||
make -j bench_random_mixed_hakmem
|
||||
|
||||
# Run 10 iterations
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
|
||||
# Record results
|
||||
cp results/mixed_10_summary.txt docs/analysis/PHASE[N]_BASELINE.txt
|
||||
```
|
||||
|
||||
#### B. Compiled-In Build (COMPILED=1)
|
||||
|
||||
```bash
|
||||
# Clean build with stats compiled IN
|
||||
make clean
|
||||
make -j EXTRA_CFLAGS='-DHAKMEM_[NAME]_STATS_COMPILED=1' bench_random_mixed_hakmem
|
||||
|
||||
# Run 10 iterations
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
|
||||
# Record results
|
||||
cp results/mixed_10_summary.txt docs/analysis/PHASE[N]_COMPILED_IN.txt
|
||||
```
|
||||
|
||||
#### C. Compare Results
|
||||
|
||||
```bash
|
||||
# Calculate delta
|
||||
scripts/compare_benchmark_results.sh \
|
||||
docs/analysis/PHASE[N]_BASELINE.txt \
|
||||
docs/analysis/PHASE[N]_COMPILED_IN.txt
|
||||
```
|
||||
|
||||
#### D. Decision Matrix
|
||||
|
||||
| Delta | Verdict | Action |
|
||||
|-------|---------|--------|
|
||||
| **+0.5% or higher** | **GO** | Keep compile-out, document win |
|
||||
| **±0.5%** | **NEUTRAL** | Keep for code cleanliness |
|
||||
| **-0.5% or lower** | **NO-GO** | Revert changes |
|
||||
|
||||
**Rationale:**
|
||||
- +0.5%: Statistically significant (HOT path impact)
|
||||
- ±0.5%: Noise range (but cleanliness still valuable)
|
||||
- -0.5%: Unexpected regression (likely measurement error, revert)
|
||||
|
||||
**Output:** `PHASE[N]_RESULTS.md` with full comparison
|
||||
|
||||
---
|
||||
|
||||
## 3. Phase Checklist Template
|
||||
|
||||
Copy this for each new phase:
|
||||
|
||||
```markdown
|
||||
## Phase [N]: [Target Description] Atomic Prune
|
||||
|
||||
**Date:** YYYY-MM-DD
|
||||
**Target:** [Atomic variable/scope name]
|
||||
**Expected Impact:** [HOT/WARM/COLD path, estimated %]
|
||||
|
||||
---
|
||||
|
||||
### Step 0: Execution Verification ✅/❌
|
||||
|
||||
- [ ] **ENV Gate Check**
|
||||
```bash
|
||||
rg "getenv.*[FEATURE]" core/
|
||||
```
|
||||
Result: [No ENV gate / Gated by X=OFF / Gated by X=ON]
|
||||
|
||||
- [ ] **Execution Counter Verification**
|
||||
```bash
|
||||
rg -n "atomic.*g_target" core/
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
grep "target_counter" results/*.txt
|
||||
```
|
||||
Result: [Counter > 0 in all runs / Counter = 0 / Not visible]
|
||||
|
||||
- [ ] **perf Profile Check (optional)**
|
||||
```bash
|
||||
perf record -g -F 99 -- ./bench_random_mixed_hakmem
|
||||
perf report | grep "target_function"
|
||||
```
|
||||
Result: [Function appears in profile / Not in profile]
|
||||
|
||||
**Verdict:** [✅ PROCEED / ❌ SKIP (reason)]
|
||||
|
||||
---
|
||||
|
||||
### Step 1: CORRECTNESS/TELEMETRY Classification
|
||||
|
||||
- [ ] **List All Atomics**
|
||||
```bash
|
||||
rg -n "atomic_(fetch_add|load|store).*g_" [target_file]
|
||||
```
|
||||
|
||||
- [ ] **Track All Usage Sites**
|
||||
```bash
|
||||
rg -n "g_atomic_var" core/
|
||||
```
|
||||
|
||||
- [ ] **Classify Each Atomic**
|
||||
|
||||
| Atomic Variable | Usage | Class | Verdict |
|
||||
|-----------------|-------|-------|---------|
|
||||
| `g_var1` | `if` condition | CORRECTNESS | ❌ DO NOT TOUCH |
|
||||
| `g_var2` | `fprintf` only | TELEMETRY | ✅ Candidate |
|
||||
|
||||
- [ ] **Document Classification Rationale**
|
||||
|
||||
**Output:** Classification table saved to `PHASE[N]_AUDIT.md`
|
||||
|
||||
---
|
||||
|
||||
### Step 2: Compile-Out Implementation
|
||||
|
||||
- [ ] **Add BuildFlags Gate**
|
||||
```c
|
||||
// core/hakmem_build_flags.h
|
||||
#ifndef HAKMEM_[NAME]_STATS_COMPILED
|
||||
# define HAKMEM_[NAME]_STATS_COMPILED 0
|
||||
#endif
|
||||
```
|
||||
|
||||
- [ ] **Wrap TELEMETRY Atomics**
|
||||
```c
|
||||
#if HAKMEM_[NAME]_STATS_COMPILED
|
||||
atomic_fetch_add_explicit(&g_stat, 1, memory_order_relaxed);
|
||||
#else
|
||||
(void)0;
|
||||
#endif
|
||||
```
|
||||
|
||||
- [ ] **Verify Compilation**
|
||||
```bash
|
||||
make clean && make -j # COMPILED=0 default
|
||||
make clean && make -j EXTRA_CFLAGS='-DHAKMEM_[NAME]_STATS_COMPILED=1'
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
### Step 3: A/B Test
|
||||
|
||||
- [ ] **Baseline Build (COMPILED=0)**
|
||||
```bash
|
||||
make clean && make -j bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
cp results/mixed_10_summary.txt docs/analysis/PHASE[N]_BASELINE.txt
|
||||
```
|
||||
|
||||
- [ ] **Compiled-In Build (COMPILED=1)**
|
||||
```bash
|
||||
make clean && make -j EXTRA_CFLAGS='-DHAKMEM_[NAME]_STATS_COMPILED=1' bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
cp results/mixed_10_summary.txt docs/analysis/PHASE[N]_COMPILED_IN.txt
|
||||
```
|
||||
|
||||
- [ ] **Compare Results**
|
||||
```bash
|
||||
scripts/compare_benchmark_results.sh \
|
||||
docs/analysis/PHASE[N]_BASELINE.txt \
|
||||
docs/analysis/PHASE[N]_COMPILED_IN.txt
|
||||
```
|
||||
|
||||
- [ ] **Record Verdict**
|
||||
- Delta: [+X.XX%]
|
||||
- Verdict: [GO / NEUTRAL / NO-GO]
|
||||
- Rationale: [...]
|
||||
|
||||
**Output:** `PHASE[N]_RESULTS.md` with full comparison
|
||||
|
||||
---
|
||||
|
||||
### Deliverables
|
||||
|
||||
- [ ] `PHASE[N]_AUDIT.md` - Classification and execution verification
|
||||
- [ ] `PHASE[N]_BASELINE.txt` - Baseline benchmark results
|
||||
- [ ] `PHASE[N]_COMPILED_IN.txt` - Compiled-in benchmark results
|
||||
- [ ] `PHASE[N]_RESULTS.md` - A/B comparison and verdict
|
||||
- [ ] Update `ATOMIC_PRUNE_CUMULATIVE_SUMMARY.md` with Phase [N] results
|
||||
- [ ] Update `CURRENT_TASK.md` with next phase
|
||||
|
||||
---
|
||||
|
||||
### Notes
|
||||
|
||||
[Add any phase-specific observations, gotchas, or learnings here]
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## 4. Success Criteria
|
||||
|
||||
A phase is considered **GO** if:
|
||||
1. ✅ Step 0: Execution verified (counter > 0 or perf profile hit)
|
||||
2. ✅ Step 1: Pure TELEMETRY classification (no CORRECTNESS atomics)
|
||||
3. ✅ Step 2: Clean compile-out implementation (no link-out)
|
||||
4. ✅ Step 3: +0.5% or higher performance delta
|
||||
|
||||
A phase is **NO-OP** if:
|
||||
- ❌ Step 0: Not executed in benchmark (Phase 29)
|
||||
- ❌ Step 1: CORRECTNESS atomic (Phase 28)
|
||||
- ❌ Step 3: Delta within ±0.5% noise range
|
||||
|
||||
---
|
||||
|
||||
## 5. Anti-Patterns to Avoid
|
||||
|
||||
### ❌ Skipping Execution Verification (Phase 29)
|
||||
**Problem:** Optimizing ENV-gated code that never runs
|
||||
**Solution:** Always run Step 0 before any work
|
||||
|
||||
### ❌ Assuming Counter = Telemetry (Phase 28)
|
||||
**Problem:** Flow control atomics look like counters
|
||||
**Solution:** Check all usage sites, especially `if` conditions
|
||||
|
||||
### ❌ Link-Out Instead of Compile-Out (Phase 22-2)
|
||||
**Problem:** ABI breaks, mysterious link errors
|
||||
**Solution:** Use `#if` preprocessor guards, never remove `.o` files
|
||||
|
||||
### ❌ Runtime Flags for Stats (not attempted, but common mistake)
|
||||
**Problem:** `if (g_enable_stats)` adds branch overhead
|
||||
**Solution:** Build-level `#if` has zero runtime cost
|
||||
|
||||
---
|
||||
|
||||
## 6. Expected Impact by Path Type
|
||||
|
||||
Based on Phase 24-29 results:
|
||||
|
||||
| Path Type | Expected Delta | Example Phases |
|
||||
|-----------|----------------|----------------|
|
||||
| **HOT** (alloc/free fast path) | **+0.5% to +1.5%** | Phase 24 (+0.93%), Phase 25 (+1.07%) |
|
||||
| **WARM** (TLS cache hit) | **+0.2% to +0.8%** | Phase 27 (+0.74%) |
|
||||
| **COLD** (slow path, rare events) | **±0.0% to +0.2%** | Phase 26 (NEUTRAL, cleanliness) |
|
||||
| **ENV-gated OFF** | **0.0% (no-op)** | Phase 29 (pool v2) |
|
||||
| **CORRECTNESS** | **Undefined (DO NOT TOUCH)** | Phase 28 (bg_spill_len) |
|
||||
|
||||
---
|
||||
|
||||
## 7. Tools and Scripts
|
||||
|
||||
### Execution Verification
|
||||
```bash
|
||||
# ENV gate check
|
||||
rg "getenv.*FEATURE" core/
|
||||
|
||||
# Counter check (requires benchmark run)
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
grep "counter_name" results/*.txt
|
||||
|
||||
# perf profile
|
||||
perf record -g -F 99 -- ./bench_random_mixed_hakmem
|
||||
perf report | grep "function_name"
|
||||
```
|
||||
|
||||
### Classification Audit
|
||||
```bash
|
||||
# List all atomics in scope
|
||||
rg -n "atomic_(fetch_add|load|store|compare_exchange)" [file]
|
||||
|
||||
# Track variable usage
|
||||
rg -n "g_variable_name" core/
|
||||
|
||||
# Find if conditions
|
||||
rg -n "if.*g_variable" core/
|
||||
```
|
||||
|
||||
### A/B Testing
|
||||
```bash
|
||||
# Baseline
|
||||
make clean && make -j bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
|
||||
# Compiled-in
|
||||
make clean && make -j EXTRA_CFLAGS='-DHAKMEM_FEATURE_COMPILED=1' bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
|
||||
# Compare (if script exists)
|
||||
scripts/compare_benchmark_results.sh baseline.txt compiled_in.txt
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## 8. Governance
|
||||
|
||||
**When to Use This Procedure:**
|
||||
- Any new atomic prune phase (Phase 31+)
|
||||
- Reviewing existing compile-out flags for consistency
|
||||
- Training new contributors on atomic optimization
|
||||
|
||||
**When to Skip:**
|
||||
- Non-atomic optimizations (inlining, data structure changes)
|
||||
- Known CORRECTNESS atomics (Step 1 already failed)
|
||||
- Features explicitly marked "do not optimize"
|
||||
|
||||
**Document Updates:**
|
||||
- This procedure should be updated after each phase if new patterns emerge
|
||||
- Phase results should update `ATOMIC_PRUNE_CUMULATIVE_SUMMARY.md`
|
||||
- New anti-patterns should be added to Section 5
|
||||
|
||||
---
|
||||
|
||||
## 9. References
|
||||
|
||||
- **Phase 24 Results:** `docs/analysis/PHASE24_ALLOC_GATE_STATS_RESULTS.md` (+0.93%)
|
||||
- **Phase 25 Results:** `docs/analysis/PHASE25_FREE_PATH_STATS_RESULTS.md` (+1.07%)
|
||||
- **Phase 27 Results:** `docs/analysis/PHASE27_TINY_FRONT_STATS_RESULTS.md` (+0.74%)
|
||||
- **Phase 28 NO-OP:** `docs/analysis/PHASE28_BGTHREAD_ATOMIC_AUDIT.md` (CORRECTNESS)
|
||||
- **Phase 29 NO-OP:** `docs/analysis/PHASE29_POOL_V2_AUDIT.md` (ENV-gated)
|
||||
- **Cumulative Summary:** `docs/analysis/ATOMIC_PRUNE_CUMULATIVE_SUMMARY.md`
|
||||
|
||||
---
|
||||
|
||||
**End of Standard Procedure Document**
|
||||
|
||||
**Next:** Apply Step 0 to Phase 31 candidates to ensure execution before optimization.
|
||||
368
docs/analysis/PHASE31_RECOMMENDED_CANDIDATES.md
Normal file
368
docs/analysis/PHASE31_RECOMMENDED_CANDIDATES.md
Normal file
@ -0,0 +1,368 @@
|
||||
# Phase 31: Recommended Atomic Prune Candidates
|
||||
|
||||
**Date:** 2025-12-16
|
||||
**Status:** CANDIDATE SELECTION (Step 0 verification complete)
|
||||
**Purpose:** Select next high-impact atomic prune target based on Phase 30 standard procedure
|
||||
|
||||
---
|
||||
|
||||
## Executive Summary
|
||||
|
||||
**Audit Results:**
|
||||
- Total atomics found: 412
|
||||
- TELEMETRY candidates: 104
|
||||
- CORRECTNESS (do not touch): 24
|
||||
- UNKNOWN (needs manual review): 284
|
||||
- HOT path atomics: 16
|
||||
- WARM path atomics: 10
|
||||
|
||||
**NEW Candidates (not yet compiled out):**
|
||||
- **1 HOT path** TELEMETRY candidate
|
||||
- **3 WARM path** TELEMETRY candidates
|
||||
|
||||
**Phase 24-29 completed candidates (already done):**
|
||||
- 4 HOT path atomics already compiled out (Phase 24-27)
|
||||
|
||||
---
|
||||
|
||||
## Step 0 Verification Results
|
||||
|
||||
### Priority 1: HOT Path NEW Candidates
|
||||
|
||||
#### Candidate 1: `g_tiny_free_trace` (HOT path)
|
||||
|
||||
**Location:** `core/hakmem_tiny_free.inc:326`
|
||||
|
||||
**Code Context:**
|
||||
```c
|
||||
void hak_tiny_free(void* ptr) {
|
||||
static _Atomic int g_tiny_free_trace = 0;
|
||||
if (atomic_fetch_add_explicit(&g_tiny_free_trace, 1, memory_order_relaxed) < 128) {
|
||||
HAK_TRACE("[hak_tiny_free_enter]\n");
|
||||
}
|
||||
// Track total tiny free calls (diagnostics)
|
||||
```
|
||||
|
||||
**Classification:**
|
||||
- **Class:** TELEMETRY (trace logging only)
|
||||
- **Path:** HOT (executed on every tiny free call)
|
||||
- **Usage:** Only for `HAK_TRACE` debug macro output
|
||||
- **ENV Gate:** None (always active in HOT path)
|
||||
|
||||
**Step 0 Verification:**
|
||||
- ✅ No ENV gate blocking execution
|
||||
- ✅ In `hak_tiny_free()` - called on every tiny free operation
|
||||
- ✅ Mixed benchmark heavily exercises tiny free path
|
||||
- ✅ Confirmed: Executes thousands of times per benchmark run
|
||||
|
||||
**Step 1 Pre-Classification:**
|
||||
- Pure TELEMETRY: Only used in trace macro (logging)
|
||||
- Not in any `if` condition for control flow
|
||||
- Removing it changes no behavior (only limits trace output to first 128 calls)
|
||||
|
||||
**Expected Impact:** **+0.5% to +1.0%** (HOT path, similar to Phase 25 free stats: +1.07%)
|
||||
|
||||
**Recommendation:** **TOP PRIORITY for Phase 31**
|
||||
|
||||
---
|
||||
|
||||
### Priority 2: WARM Path NEW Candidates
|
||||
|
||||
#### Candidate 2A: `rel_logs` (WARM path)
|
||||
|
||||
**Location:**
|
||||
- `core/hakmem_tiny_refill.inc.h:106`
|
||||
- `core/box/warm_pool_prefill_box.h:35`
|
||||
|
||||
**Code Context:**
|
||||
```c
|
||||
static inline void warm_prefill_log_c7_meta(const char* tag, TinyTLSSlab* tls) {
|
||||
if (!tls || !tls->ss) return;
|
||||
if (!warm_prefill_log_enabled()) return; // ENV gate check
|
||||
#if HAKMEM_BUILD_RELEASE
|
||||
static _Atomic uint32_t rel_logs = 0;
|
||||
uint32_t n = atomic_fetch_add_explicit(&rel_logs, 1, memory_order_relaxed);
|
||||
if (n < 4) {
|
||||
fprintf(stderr, "[REL_C7_USED_ASSIGN] tag=%s used=%u ...\n", tag, ...);
|
||||
}
|
||||
#else
|
||||
// Debug version (different logging)
|
||||
#endif
|
||||
}
|
||||
```
|
||||
|
||||
**Classification:**
|
||||
- **Class:** TELEMETRY (fprintf logging only)
|
||||
- **Path:** WARM (refill operations)
|
||||
- **Usage:** Only for limiting log output to first 4 calls
|
||||
- **ENV Gate:** `HAKMEM_TINY_WARM_LOG` (OFF by default)
|
||||
|
||||
**Step 0 Verification:**
|
||||
- ⚠️ ENV gated by `warm_prefill_log_enabled()` → checks `HAKMEM_TINY_WARM_LOG`
|
||||
- ❌ ENV default: OFF (not set in benchmark environment)
|
||||
- ❌ Execution in benchmark: **LIKELY ZERO** (gated by ENV check)
|
||||
|
||||
**Expected Impact:** **0.0% (NO-OP)** - ENV gated like Phase 29 pool v2
|
||||
|
||||
**Recommendation:** **SKIP** (Phase 29 lesson: ENV-gated code = no-op)
|
||||
|
||||
---
|
||||
|
||||
#### Candidate 2B: `dbg_logs` (WARM path)
|
||||
|
||||
**Location:**
|
||||
- `core/hakmem_tiny_refill.inc.h:118`
|
||||
- `core/box/warm_pool_prefill_box.h:53`
|
||||
|
||||
**Code Context:**
|
||||
```c
|
||||
static inline void warm_prefill_dbg_c7_meta(const char* tag, TinyTLSSlab* tls) {
|
||||
if (!tls || !tls->ss) return;
|
||||
if (!warm_prefill_log_enabled()) return; // ENV gate check
|
||||
#if HAKMEM_BUILD_RELEASE
|
||||
// rel_logs version
|
||||
#else
|
||||
static _Atomic uint32_t dbg_logs = 0;
|
||||
uint32_t n = atomic_fetch_add_explicit(&dbg_logs, 1, memory_order_relaxed);
|
||||
if (n < 4) {
|
||||
fprintf(stderr, "[DBG_C7_USED_ASSIGN] tag=%s used=%u ...\n", tag, ...);
|
||||
}
|
||||
#endif
|
||||
}
|
||||
```
|
||||
|
||||
**Classification:**
|
||||
- **Class:** TELEMETRY (fprintf logging only)
|
||||
- **Path:** WARM (refill operations)
|
||||
- **Usage:** Only for limiting log output to first 4 calls
|
||||
- **ENV Gate:** `HAKMEM_TINY_WARM_LOG` (OFF by default)
|
||||
- **Build Gate:** `#if HAKMEM_BUILD_RELEASE` - dbg_logs only in debug builds
|
||||
|
||||
**Step 0 Verification:**
|
||||
- ⚠️ ENV gated by `warm_prefill_log_enabled()` → checks `HAKMEM_TINY_WARM_LOG`
|
||||
- ❌ ENV default: OFF (not set in benchmark environment)
|
||||
- ⚠️ Build gated: Only in debug builds (opposite branch from `rel_logs`)
|
||||
- ❌ Execution in benchmark: **LIKELY ZERO** (ENV gate + wrong build branch)
|
||||
|
||||
**Expected Impact:** **0.0% (NO-OP)** - ENV gated + debug build only
|
||||
|
||||
**Recommendation:** **SKIP** (same ENV gate issue as `rel_logs`)
|
||||
|
||||
---
|
||||
|
||||
#### Candidate 2C: `g_p0_class_oob_log` (WARM path)
|
||||
|
||||
**Location:** `core/hakmem_tiny_refill_p0.inc.h:41`
|
||||
|
||||
**Code Context:**
|
||||
```c
|
||||
static inline int sll_refill_batch_from_ss(int class_idx, int max_take) {
|
||||
HAK_CHECK_CLASS_IDX(class_idx, "sll_refill_batch_from_ss");
|
||||
if (__builtin_expect(class_idx < 0 || class_idx >= TINY_NUM_CLASSES, 0)) {
|
||||
static _Atomic int g_p0_class_oob_log = 0;
|
||||
if (atomic_fetch_add_explicit(&g_p0_class_oob_log, 1, memory_order_relaxed) == 0) {
|
||||
fprintf(stderr, "[P0_CLASS_OOB] class_idx=%d max_take=%d\n", class_idx, max_take);
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
// ... normal path ...
|
||||
}
|
||||
```
|
||||
|
||||
**Classification:**
|
||||
- **Class:** TELEMETRY (error logging only)
|
||||
- **Path:** WARM (P0 batch refill)
|
||||
- **Usage:** Only for `fprintf` on first error occurrence
|
||||
- **ENV Gate:** None
|
||||
|
||||
**Step 0 Verification:**
|
||||
- ✅ No ENV gate blocking execution
|
||||
- ⚠️ In error path: `if (class_idx < 0 || class_idx >= TINY_NUM_CLASSES)`
|
||||
- ⚠️ Error condition should be rare (out-of-bounds class index)
|
||||
- ❓ Execution frequency: **Unknown** (depends on whether benchmark triggers OOB)
|
||||
|
||||
**Expected Impact:** **±0.0% to +0.2%** (error path, likely infrequent)
|
||||
|
||||
**Recommendation:** **LOW PRIORITY** (error path, uncertain execution frequency)
|
||||
|
||||
**Action Required:** Need to verify if error path is ever hit:
|
||||
```bash
|
||||
# Add temporary counter to verify execution
|
||||
grep -n "P0_CLASS_OOB" benchmark_output.txt
|
||||
# OR check if class_idx is ever out of bounds
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## Phase 31 Recommendation: TOP 3 Candidates
|
||||
|
||||
### Tier S: Immediate Action (HIGH Impact Expected)
|
||||
|
||||
**#1: `g_tiny_free_trace` (HOT path, TELEMETRY)**
|
||||
- **Location:** `core/hakmem_tiny_free.inc:326`
|
||||
- **Path:** HOT (every tiny free call)
|
||||
- **Expected Impact:** **+0.5% to +1.0%**
|
||||
- **Execution Verified:** ✅ YES (no ENV gate, core free path)
|
||||
- **Classification:** Pure TELEMETRY (trace macro only)
|
||||
- **Precedent:** Similar to Phase 25 free stats (+1.07%)
|
||||
- **Action:** Proceed to Phase 31 implementation
|
||||
|
||||
**Rationale:**
|
||||
- Only NEW HOT path candidate remaining
|
||||
- No ENV gate blocking execution
|
||||
- Similar profile to successful Phase 25 (free path stats)
|
||||
- High confidence of GO result
|
||||
|
||||
---
|
||||
|
||||
### Tier B: Consider Later (Uncertain Execution)
|
||||
|
||||
**#2: `g_p0_class_oob_log` (WARM path, error logging)**
|
||||
- **Location:** `core/hakmem_tiny_refill_p0.inc.h:41`
|
||||
- **Path:** WARM (but error path)
|
||||
- **Expected Impact:** **±0.0% to +0.2%**
|
||||
- **Execution Verified:** ❓ UNCERTAIN (error path, needs verification)
|
||||
- **Classification:** TELEMETRY (fprintf only)
|
||||
- **Action:** Verify execution first, then consider for Phase 32
|
||||
|
||||
---
|
||||
|
||||
### Tier C: Skip (ENV-gated, no execution)
|
||||
|
||||
**#3: `rel_logs` + `dbg_logs` (WARM path, ENV-gated)**
|
||||
- **Location:** `core/box/warm_pool_prefill_box.h`, `core/hakmem_tiny_refill.inc.h`
|
||||
- **Path:** WARM (refill operations)
|
||||
- **Expected Impact:** **0.0% (NO-OP)**
|
||||
- **Execution Verified:** ❌ NO (ENV gate OFF by default)
|
||||
- **Classification:** TELEMETRY (fprintf only)
|
||||
- **Action:** SKIP (Phase 29 lesson: ENV-gated = wasted effort)
|
||||
|
||||
---
|
||||
|
||||
## Phase 31 Implementation Plan
|
||||
|
||||
### Recommended Target: `g_tiny_free_trace`
|
||||
|
||||
**Step 1: CORRECTNESS/TELEMETRY Classification**
|
||||
|
||||
Already verified:
|
||||
- ✅ Pure TELEMETRY (only used in HAK_TRACE macro)
|
||||
- ✅ Not in any `if` condition for control flow
|
||||
- ✅ Removing changes no behavior
|
||||
|
||||
**Step 2: Compile-Out Implementation**
|
||||
|
||||
a) Add BuildFlags gate:
|
||||
```c
|
||||
// core/hakmem_build_flags.h
|
||||
// ========== Tiny Free Trace Atomic Prune (Phase 31) ==========
|
||||
#ifndef HAKMEM_TINY_FREE_TRACE_COMPILED
|
||||
# define HAKMEM_TINY_FREE_TRACE_COMPILED 0
|
||||
#endif
|
||||
```
|
||||
|
||||
b) Wrap atomic in `core/hakmem_tiny_free.inc`:
|
||||
```c
|
||||
void hak_tiny_free(void* ptr) {
|
||||
#if HAKMEM_TINY_FREE_TRACE_COMPILED
|
||||
static _Atomic int g_tiny_free_trace = 0;
|
||||
if (atomic_fetch_add_explicit(&g_tiny_free_trace, 1, memory_order_relaxed) < 128) {
|
||||
HAK_TRACE("[hak_tiny_free_enter]\n");
|
||||
}
|
||||
#else
|
||||
(void)0; // No-op when compiled out
|
||||
#endif
|
||||
// ... rest of function ...
|
||||
}
|
||||
```
|
||||
|
||||
**Step 3: A/B Test**
|
||||
|
||||
Baseline (COMPILED=0):
|
||||
```bash
|
||||
make clean && make -j bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
```
|
||||
|
||||
Compiled-in (COMPILED=1):
|
||||
```bash
|
||||
make clean && make -j EXTRA_CFLAGS='-DHAKMEM_TINY_FREE_TRACE_COMPILED=1' bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
```
|
||||
|
||||
**Expected Result:** +0.5% to +1.0% (GO)
|
||||
|
||||
---
|
||||
|
||||
## Alternative: Broader Atomic Audit
|
||||
|
||||
If `g_tiny_free_trace` yields NO-GO, consider:
|
||||
|
||||
1. **Manual review of UNKNOWN atomics (284 candidates)**
|
||||
- Many may be misclassified by naming heuristics
|
||||
- Potential hidden TELEMETRY candidates
|
||||
- Requires deeper code inspection
|
||||
|
||||
2. **Expand to COLD path TELEMETRY**
|
||||
- 386 COLD path atomics total
|
||||
- Lower impact but code cleanliness benefit
|
||||
- Example: Background thread stats, rare error paths
|
||||
|
||||
3. **Focus on non-atomic optimizations**
|
||||
- Phase 30 procedure is for atomics only
|
||||
- Branch optimization, inlining, etc. require different approach
|
||||
|
||||
---
|
||||
|
||||
## Summary Table
|
||||
|
||||
| Candidate | Path | Class | ENV Gate | Exec Verified | Expected Impact | Priority |
|
||||
|-----------|------|-------|----------|---------------|-----------------|----------|
|
||||
| `g_tiny_free_trace` | HOT | TELEMETRY | None | ✅ YES | **+0.5% to +1.0%** | **#1 (TOP)** |
|
||||
| `g_p0_class_oob_log` | WARM | TELEMETRY | None | ❓ UNCERTAIN | ±0.0% to +0.2% | #2 (verify first) |
|
||||
| `rel_logs` | WARM | TELEMETRY | ❌ OFF | ❌ NO | 0.0% (NO-OP) | SKIP |
|
||||
| `dbg_logs` | WARM | TELEMETRY | ❌ OFF | ❌ NO | 0.0% (NO-OP) | SKIP |
|
||||
|
||||
---
|
||||
|
||||
## Lessons Applied from Phase 30 Standard Procedure
|
||||
|
||||
✅ **Step 0 Execution Verification:**
|
||||
- Checked all candidates for ENV gates
|
||||
- Identified 2 ENV-gated candidates (rel_logs, dbg_logs) → SKIP
|
||||
- Verified HOT path candidate has no execution blockers
|
||||
|
||||
✅ **Phase 28 Lesson (CORRECTNESS check):**
|
||||
- Verified `g_tiny_free_trace` not in `if` conditions
|
||||
- Confirmed pure TELEMETRY usage (trace macro only)
|
||||
|
||||
✅ **Phase 29 Lesson (ENV gate):**
|
||||
- Eliminated `rel_logs` and `dbg_logs` due to ENV gate
|
||||
- Avoided wasting effort on non-executing code
|
||||
|
||||
✅ **Phase 24-27 Pattern (HOT path impact):**
|
||||
- Selected HOT path candidate for maximum impact
|
||||
- Expected similar gains to Phase 25 free stats
|
||||
|
||||
---
|
||||
|
||||
## Next Steps
|
||||
|
||||
1. **Proceed with Phase 31: `g_tiny_free_trace` atomic prune**
|
||||
- Follow Phase 30 standard procedure (4 steps)
|
||||
- Expected result: GO (+0.5% to +1.0%)
|
||||
|
||||
2. **If Phase 31 yields GO:**
|
||||
- Update cumulative summary (+3.24% to +3.74% total)
|
||||
- Move to Phase 32: Verify `g_p0_class_oob_log` execution
|
||||
|
||||
3. **If Phase 31 yields NO-GO:**
|
||||
- Investigate why (measurement noise? unusual workload?)
|
||||
- Consider manual audit of UNKNOWN atomics (284 candidates)
|
||||
- Shift focus to non-atomic optimizations
|
||||
|
||||
---
|
||||
|
||||
**Recommendation:** **Proceed with Phase 31 targeting `g_tiny_free_trace`**
|
||||
|
||||
**Confidence Level:** High (HOT path, no blockers, proven pattern)
|
||||
405
docs/analysis/PHASE31_TINY_FREE_TRACE_ATOMIC_PRUNE_RESULTS.md
Normal file
405
docs/analysis/PHASE31_TINY_FREE_TRACE_ATOMIC_PRUNE_RESULTS.md
Normal file
@ -0,0 +1,405 @@
|
||||
# Phase 31: Tiny Free Trace Atomic Prune - Results
|
||||
|
||||
**Date:** 2025-12-16
|
||||
**Type:** HOT path TELEMETRY atomic prune
|
||||
**Target:** `g_tiny_free_trace` atomic in `core/hakmem_tiny_free.inc:326`
|
||||
**Verdict:** NEUTRAL (code cleanliness adopted)
|
||||
|
||||
---
|
||||
|
||||
## Executive Summary
|
||||
|
||||
Phase 31 targeted the `g_tiny_free_trace` atomic in the HOT path (`hak_tiny_free()` entry point). A/B testing showed **NEUTRAL performance** (-0.35% mean, +0.19% median), well within noise range (±0.5%). Following Phase 26 precedent (5 atomics, -0.33%, adopted for code cleanliness), **Phase 31 is ADOPTED** with COMPILED=0 as default to reduce HOT path complexity.
|
||||
|
||||
---
|
||||
|
||||
## Background
|
||||
|
||||
### Phase 30 Selection Process
|
||||
|
||||
From 412 total atomics audited:
|
||||
- **HOT path candidates:** 16 total
|
||||
- 5 TELEMETRY (4 already compiled-out in Phases 24-27)
|
||||
- 11 UNKNOWN (require manual review)
|
||||
|
||||
**Phase 31 candidate selected:** `g_tiny_free_trace` (HOT path, TELEMETRY, TOP PRIORITY)
|
||||
|
||||
**Step 0 verification (MANDATORY):**
|
||||
- No ENV gate → always active
|
||||
- Located in `hak_tiny_free()` → executes on EVERY tiny free call
|
||||
- Mixed benchmark heavily exercises free path → high execution count
|
||||
- **Execution confirmed:** First instruction in HOT path function
|
||||
|
||||
### Target Profile
|
||||
|
||||
**Location:** `core/hakmem_tiny_free.inc:326`
|
||||
|
||||
**Original Code:**
|
||||
```c
|
||||
void hak_tiny_free(void* ptr) {
|
||||
static _Atomic int g_tiny_free_trace = 0;
|
||||
if (atomic_fetch_add_explicit(&g_tiny_free_trace, 1, memory_order_relaxed) < 128) {
|
||||
HAK_TRACE("[hak_tiny_free_enter]\n");
|
||||
}
|
||||
// ... rest of function ...
|
||||
}
|
||||
```
|
||||
|
||||
**Classification:**
|
||||
- **Class:** TELEMETRY (trace rate-limit only)
|
||||
- **Path:** HOT (every tiny free operation)
|
||||
- **Flow Control:** None (only affects `HAK_TRACE` macro output)
|
||||
- **Correctness Impact:** None
|
||||
|
||||
**Similar precedent:** Phase 25 (`g_free_ss_enter`: +1.07% GO)
|
||||
|
||||
---
|
||||
|
||||
## Implementation (4-Step Standard Procedure)
|
||||
|
||||
### Step 0: Execution Verification (Phase 29 lesson)
|
||||
|
||||
**ENV gate check:**
|
||||
```bash
|
||||
$ rg "getenv.*TRACE" core/ --type c
|
||||
# (No results - no ENV gate blocking execution)
|
||||
```
|
||||
|
||||
**Execution check:**
|
||||
- Located at entry of `hak_tiny_free()` (line 326)
|
||||
- Executes on EVERY tiny free call (no conditional bypass)
|
||||
- Mixed benchmark: ~10M+ free operations per run
|
||||
- **Verification:** PASSED (always active)
|
||||
|
||||
### Step 1: CORRECTNESS/TELEMETRY Classification (Phase 28 lesson)
|
||||
|
||||
**Full usage audit:**
|
||||
```bash
|
||||
$ rg -n "g_tiny_free_trace" core/
|
||||
core/hakmem_tiny_free.inc:326: static _Atomic int g_tiny_free_trace = 0;
|
||||
core/hakmem_tiny_free.inc:327: if (atomic_fetch_add_explicit(&g_tiny_free_trace, 1, memory_order_relaxed) < 128) {
|
||||
```
|
||||
|
||||
**Analysis:**
|
||||
- Only 2 uses: declaration + atomic increment
|
||||
- No `if` conditions using the counter value
|
||||
- Only affects `HAK_TRACE` printf (debug macro)
|
||||
- **Classification:** Pure TELEMETRY ✅
|
||||
|
||||
### Step 2: Compile-Out Implementation
|
||||
|
||||
**File 1:** `core/hakmem_build_flags.h`
|
||||
|
||||
**Added:**
|
||||
```c
|
||||
// ------------------------------------------------------------
|
||||
// Phase 31: Tiny Free Trace Atomic Prune (Compile-out trace atomic)
|
||||
// ------------------------------------------------------------
|
||||
// Tiny Free Trace: Compile gate (default OFF = compile-out)
|
||||
// Set to 1 for research builds that need free path trace diagnostics
|
||||
// Target: g_tiny_free_trace atomic in core/hakmem_tiny_free.inc:326
|
||||
// Impact: HOT path atomic (every free operation)
|
||||
// Expected improvement: +0.5% to +1.0% (similar to Phase 25: +1.07%)
|
||||
#ifndef HAKMEM_TINY_FREE_TRACE_COMPILED
|
||||
# define HAKMEM_TINY_FREE_TRACE_COMPILED 0
|
||||
#endif
|
||||
```
|
||||
|
||||
**File 2:** `core/hakmem_tiny_free.inc:326`
|
||||
|
||||
**Before:**
|
||||
```c
|
||||
void hak_tiny_free(void* ptr) {
|
||||
static _Atomic int g_tiny_free_trace = 0;
|
||||
if (atomic_fetch_add_explicit(&g_tiny_free_trace, 1, memory_order_relaxed) < 128) {
|
||||
HAK_TRACE("[hak_tiny_free_enter]\n");
|
||||
}
|
||||
// ... rest of function ...
|
||||
}
|
||||
```
|
||||
|
||||
**After:**
|
||||
```c
|
||||
void hak_tiny_free(void* ptr) {
|
||||
#if HAKMEM_TINY_FREE_TRACE_COMPILED
|
||||
static _Atomic int g_tiny_free_trace = 0;
|
||||
if (atomic_fetch_add_explicit(&g_tiny_free_trace, 1, memory_order_relaxed) < 128) {
|
||||
HAK_TRACE("[hak_tiny_free_enter]\n");
|
||||
}
|
||||
#else
|
||||
(void)0; // No-op when trace compiled out
|
||||
#endif
|
||||
// ... rest of function ...
|
||||
}
|
||||
```
|
||||
|
||||
**Include verification:**
|
||||
- `hakmem_build_flags.h` included transitively via `tiny_front_config_box.h`
|
||||
- No explicit include needed
|
||||
|
||||
### Step 3: A/B Test (Build-Level Comparison)
|
||||
|
||||
**Baseline (COMPILED=0, default - trace compiled-out):**
|
||||
```bash
|
||||
make clean && make -j bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
```
|
||||
|
||||
**Compiled-in (COMPILED=1, research - trace active):**
|
||||
```bash
|
||||
make clean && make -j EXTRA_CFLAGS='-DHAKMEM_TINY_FREE_TRACE_COMPILED=1' bench_random_mixed_hakmem
|
||||
scripts/run_mixed_10_cleanenv.sh
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## A/B Test Results
|
||||
|
||||
### Raw Data (10-run clean environment)
|
||||
|
||||
**Baseline (COMPILED=0, trace compiled-out):**
|
||||
```
|
||||
Run 1: 53432447 ops/s
|
||||
Run 2: 53846666 ops/s
|
||||
Run 3: 53256003 ops/s
|
||||
Run 4: 54007573 ops/s
|
||||
Run 5: 54132468 ops/s
|
||||
Run 6: 53937278 ops/s
|
||||
Run 7: 53752216 ops/s
|
||||
Run 8: 53106138 ops/s
|
||||
Run 9: 53861749 ops/s
|
||||
Run 10: 53052398 ops/s
|
||||
```
|
||||
|
||||
**Compiled-in (COMPILED=1, trace active):**
|
||||
```
|
||||
Run 1: 53667388 ops/s
|
||||
Run 2: 53623799 ops/s
|
||||
Run 3: 54099595 ops/s
|
||||
Run 4: 53993106 ops/s
|
||||
Run 5: 53530214 ops/s
|
||||
Run 6: 54275707 ops/s
|
||||
Run 7: 53726604 ops/s
|
||||
Run 8: 53607801 ops/s
|
||||
Run 9: 54122912 ops/s
|
||||
Run 10: 53630312 ops/s
|
||||
```
|
||||
|
||||
### Statistical Analysis
|
||||
|
||||
| Metric | Baseline (COMPILED=0) | Compiled-in (COMPILED=1) | Difference |
|
||||
|--------|----------------------|-------------------------|------------|
|
||||
| **Mean** | 53,638,493.60 ops/s | 53,827,743.80 ops/s | **-0.35%** |
|
||||
| **Median** | 53,799,441.00 ops/s | 53,696,996.00 ops/s | **+0.19%** |
|
||||
| **Stdev** | 393,174.93 (0.73%) | 267,178.23 (0.50%) | - |
|
||||
|
||||
**Difference interpretation:**
|
||||
- **Mean:** Baseline -0.35% (SLOWER, but within noise)
|
||||
- **Median:** Baseline +0.19% (FASTER, but within noise)
|
||||
- **Verdict range:** Both within ±0.5% NEUTRAL threshold
|
||||
|
||||
---
|
||||
|
||||
## Verdict
|
||||
|
||||
### Performance: NEUTRAL
|
||||
|
||||
**Criteria:**
|
||||
- GO: +0.5% or more (compile-out wins)
|
||||
- NEUTRAL: ±0.5% (no significant difference)
|
||||
- NO-GO: -0.5% or worse (compile-out loses)
|
||||
|
||||
**Result:** NEUTRAL (-0.35% mean, +0.19% median)
|
||||
|
||||
**Analysis:**
|
||||
- Mean shows slight regression (-0.35%), median shows slight improvement (+0.19%)
|
||||
- Conflicting signals suggest **measurement noise** rather than true effect
|
||||
- Standard deviation overlap confirms lack of statistical significance
|
||||
- Similar to Phase 26 pattern (-0.33%, 5 atomics, NEUTRAL)
|
||||
|
||||
### Decision: ADOPTED (COMPILED=0 default)
|
||||
|
||||
**Rationale (following Phase 26 precedent):**
|
||||
|
||||
1. **Code Cleanliness:**
|
||||
- Removes unused TELEMETRY atomic from HOT path
|
||||
- Reduces complexity at `hak_tiny_free()` entry point
|
||||
- No correctness impact (pure trace macro)
|
||||
|
||||
2. **Consistency:**
|
||||
- Phase 26 precedent: -0.33% NEUTRAL result adopted for cleanliness
|
||||
- Phase 31: -0.35% NEUTRAL result follows same logic
|
||||
- Maintains atomic prune momentum (Phases 24-31)
|
||||
|
||||
3. **Research Flexibility:**
|
||||
- `COMPILED=1` still available for trace diagnostics
|
||||
- No functionality lost, only default changed
|
||||
- Easy revert if needed (`make EXTRA_CFLAGS=-DHAKMEM_TINY_FREE_TRACE_COMPILED=1`)
|
||||
|
||||
4. **Why Not NO-GO?**
|
||||
- Median +0.19% (slight win, not loss)
|
||||
- Mean -0.35% within noise range (±0.5% threshold)
|
||||
- Phase 26 set precedent: NEUTRAL + cleanliness = ADOPT
|
||||
|
||||
---
|
||||
|
||||
## Comparison: Phase 25 vs Phase 31
|
||||
|
||||
**Phase 25:** `g_free_ss_enter` (free stats atomic)
|
||||
- **Location:** `tiny_superslab_free.inc.h:25` (entry point)
|
||||
- **Result:** +1.07% (GO)
|
||||
- **Path:** Same HOT path (free entry)
|
||||
- **Similarity:** Both trace/stats atomics at free entry
|
||||
|
||||
**Phase 31:** `g_tiny_free_trace` (trace rate-limit atomic)
|
||||
- **Location:** `hakmem_tiny_free.inc:326` (entry point)
|
||||
- **Result:** -0.35% mean, +0.19% median (NEUTRAL)
|
||||
- **Path:** Same HOT path (free entry)
|
||||
- **Difference:** Rate-limited (128 calls) vs always-increment
|
||||
|
||||
**Why different results?**
|
||||
|
||||
1. **Execution frequency:**
|
||||
- Phase 25: EVERY free call increments stats
|
||||
- Phase 31: EVERY free call increments, but trace only 128 times
|
||||
- **Hypothesis:** Phase 25's always-active stats had higher overhead
|
||||
|
||||
2. **Atomic placement:**
|
||||
- Phase 25: Inside `hak_tiny_free_superslab()` (deeper in call stack)
|
||||
- Phase 31: First instruction in `hak_tiny_free()` (entry point)
|
||||
- **Hypothesis:** Entry point atomic may be better optimized by compiler
|
||||
|
||||
3. **Measurement variance:**
|
||||
- Phase 25: Clear +1.07% signal above noise
|
||||
- Phase 31: -0.35% / +0.19% conflicting signals (noise)
|
||||
- **Conclusion:** Phase 31 likely true NEUTRAL, not hidden win
|
||||
|
||||
---
|
||||
|
||||
## Lessons Learned
|
||||
|
||||
### 1. HOT Path ≠ Guaranteed Win
|
||||
|
||||
**Previous assumption (from Phase 25):**
|
||||
- HOT path TELEMETRY atomic → +0.5% to +1.0% expected
|
||||
|
||||
**Phase 31 reality:**
|
||||
- HOT path TELEMETRY atomic → NEUTRAL (±0.0%)
|
||||
|
||||
**Insight:**
|
||||
- Not all HOT path atomics have measurable overhead
|
||||
- Rate-limited trace (128 calls) may be optimized away by compiler
|
||||
- Entry point placement may reduce overhead vs mid-function
|
||||
|
||||
### 2. NEUTRAL + Cleanliness = ADOPT
|
||||
|
||||
**Established precedent (Phase 26):**
|
||||
- 5 diagnostic atomics, -0.33% NEUTRAL result
|
||||
- Adopted for code cleanliness despite no performance win
|
||||
|
||||
**Phase 31 confirms:**
|
||||
- -0.35% NEUTRAL result, same adoption logic
|
||||
- Code cleanliness is valid secondary criterion
|
||||
- Maintains atomic prune momentum (Phases 24-31)
|
||||
|
||||
### 3. Step 0 (Execution Verification) Essential
|
||||
|
||||
**Phase 31 validated:**
|
||||
- Step 0 confirmed no ENV gate → always active
|
||||
- Prevented Phase 29 "empty bench" scenario
|
||||
- Standard procedure working as designed
|
||||
|
||||
---
|
||||
|
||||
## Next Steps
|
||||
|
||||
### Phase 32 Candidate: `g_hak_tiny_free_calls`
|
||||
|
||||
**Location:** `core/hakmem_tiny_free.inc:335` (same function, 9 lines after Phase 31 target)
|
||||
|
||||
**Code context:**
|
||||
```c
|
||||
void hak_tiny_free(void* ptr) {
|
||||
#if HAKMEM_TINY_FREE_TRACE_COMPILED
|
||||
// Phase 31 target (now compiled-out)
|
||||
#endif
|
||||
// Track total tiny free calls (diagnostics)
|
||||
extern _Atomic uint64_t g_hak_tiny_free_calls;
|
||||
atomic_fetch_add_explicit(&g_hak_tiny_free_calls, 1, memory_order_relaxed); // ← Phase 32 target
|
||||
// ... rest of function ...
|
||||
}
|
||||
```
|
||||
|
||||
**Profile:**
|
||||
- **Path:** HOT (every tiny free call, same as Phase 31)
|
||||
- **Classification:** TELEMETRY (diagnostic counter, no flow control)
|
||||
- **Expected:** +0.3% to +0.7% (smaller than Phase 25, similar to Phase 31)
|
||||
- **Step 0 verification needed:** Check for ENV gate, confirm execution
|
||||
|
||||
**Alternative candidates:**
|
||||
- Manual review of UNKNOWN atomics (284 candidates from Phase 30 audit)
|
||||
- Lower priority than confirmed HOT path targets
|
||||
|
||||
---
|
||||
|
||||
## Files Modified
|
||||
|
||||
### Code Changes
|
||||
|
||||
1. **`core/hakmem_build_flags.h`**
|
||||
- Added `HAKMEM_TINY_FREE_TRACE_COMPILED` flag (default OFF)
|
||||
- Lines 363-373
|
||||
|
||||
2. **`core/hakmem_tiny_free.inc`**
|
||||
- Wrapped `g_tiny_free_trace` atomic in `#if HAKMEM_TINY_FREE_TRACE_COMPILED`
|
||||
- Lines 326-333
|
||||
|
||||
### Documentation
|
||||
|
||||
1. **`docs/analysis/PHASE31_TINY_FREE_TRACE_ATOMIC_PRUNE_RESULTS.md`** (this file)
|
||||
- A/B test results
|
||||
- NEUTRAL verdict + code cleanliness adoption
|
||||
- Phase 32 candidate proposal
|
||||
|
||||
2. **`docs/analysis/ATOMIC_PRUNE_CUMULATIVE_SUMMARY.md`** (to be updated)
|
||||
- Phase 24-31 cumulative summary
|
||||
- Updated precedents section
|
||||
- Phase 32 roadmap
|
||||
|
||||
3. **`CURRENT_TASK.md`** (to be updated)
|
||||
- Phase 31 completion
|
||||
- Phase 32 candidate recommendation
|
||||
|
||||
---
|
||||
|
||||
## Cumulative Progress (Phases 24-31)
|
||||
|
||||
| Phase | Target | Atomics | Result | Status |
|
||||
|-------|--------|---------|--------|--------|
|
||||
| **24** | Tiny Class Stats (OBSERVE) | 5 | **+0.93%** | GO ✅ |
|
||||
| **25** | Free Stats (`g_free_ss_enter`) | 1 | **+1.07%** | GO ✅ |
|
||||
| **26** | Hot Path Diagnostics | 5 | **-0.33%** | NEUTRAL ✅ |
|
||||
| **27** | Unified Cache Stats | 6 | **+0.74%** | GO ✅ |
|
||||
| **28** | Background Spill Queue | 8 | N/A | NO-OP ✅ |
|
||||
| **29** | Pool Hotbox v2 Stats | 12 | **0.00%** | NO-OP ✅ |
|
||||
| **30** | Standard Procedure | 412 audit | N/A | PROCEDURE ✅ |
|
||||
| **31** | Tiny Free Trace | 1 | **-0.35%** | NEUTRAL ✅ |
|
||||
| **Total** | **18 atomics removed** | **+2.74%** | **net cumulative** | **✅** |
|
||||
|
||||
**Net cumulative gain:** +2.74% (Phases 24+25+27, excluding NEUTRAL 26+31)
|
||||
|
||||
**Note:** Phase 26 and 31 NEUTRAL results do not degrade cumulative gain (no regression).
|
||||
|
||||
---
|
||||
|
||||
## Conclusion
|
||||
|
||||
Phase 31 demonstrates that **not all HOT path TELEMETRY atomics have measurable overhead**. While Phase 25 (`g_free_ss_enter`) delivered +1.07%, Phase 31 (`g_tiny_free_trace`) showed NEUTRAL performance (-0.35% mean, +0.19% median). Following Phase 26 precedent, **Phase 31 is ADOPTED** with COMPILED=0 as default for **code cleanliness** benefits.
|
||||
|
||||
**Key takeaways:**
|
||||
1. HOT path location does not guarantee performance wins
|
||||
2. NEUTRAL + code cleanliness is valid adoption criterion (Phase 26/31 pattern)
|
||||
3. Standard 4-step procedure successfully prevented false positives (Step 0 execution check)
|
||||
4. Phase 32 candidate ready: `g_hak_tiny_free_calls` (same HOT path, 9 lines below)
|
||||
|
||||
**Recommendation:** Proceed to Phase 32 (`g_hak_tiny_free_calls`) following same 4-step procedure.
|
||||
Reference in New Issue
Block a user