52386401b3
Major Features: - Debug counter infrastructure for Refill Stage tracking - Free Pipeline counters (ss_local, ss_remote, tls_sll) - Diagnostic counters for early return analysis - Unified larson.sh benchmark runner with profiles - Phase 6-3 regression analysis documentation Bug Fixes: - Fix SuperSlab disabled by default (HAKMEM_TINY_USE_SUPERSLAB) - Fix profile variable naming consistency - Add .gitignore patterns for large files Performance: - Phase 6-3: 4.79 M ops/s (has OOM risk) - With SuperSlab: 3.13 M ops/s (+19% improvement) This is a clean repository without large log files. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
304 lines
8.7 KiB
Markdown
304 lines
8.7 KiB
Markdown
# HAKMEM Tiny Pool - Performance Analysis Index
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**Date**: 2025-10-26
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**Session**: Post-getenv Fix Analysis
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**Status**: Analysis Complete - Optimization Recommended
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---
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## Quick Navigation
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### For Immediate Action
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- **[OPTIMIZATION_NEXT_STEPS.md](./OPTIMIZATION_NEXT_STEPS.md)** - Implementation guide for next optimization
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- **[PERF_SUMMARY.txt](./PERF_SUMMARY.txt)** - One-page executive summary
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### For Detailed Review
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- **[PERF_POST_GETENV_ANALYSIS.md](./PERF_POST_GETENV_ANALYSIS.md)** - Complete analysis with Q&A
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- **[BOTTLENECK_COMPARISON.txt](./BOTTLENECK_COMPARISON.txt)** - Before/after comparison
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### Raw Performance Data
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- `perf_post_getenv.data` - Perf recording (1 GB)
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- `perf_post_getenv_report.txt` - Top functions report
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- `perf_post_getenv_annotate.txt` - Annotated assembly
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---
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## Executive Summary
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### Achievement
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- **Eliminated getenv bottleneck**: 43.96% CPU → 0%
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- **Performance improvement**: +86% to +173% (60 → 120-164 M ops/sec)
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- **Now FASTER than glibc**: +15% to +57%
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### Current Status
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- **New #1 Bottleneck**: hak_tiny_alloc (22.75% CPU)
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- **Verdict**: Worth optimizing (2.27x above 10% threshold)
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- **Next Target**: Reduce hak_tiny_alloc to ~10% CPU
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### Recommendation
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**OPTIMIZE NEXT BOTTLENECK** - Clear path to 180-250 M ops/sec (2-3x glibc)
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---
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## File Descriptions
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### Analysis Documents
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#### PERF_POST_GETENV_ANALYSIS.md (11 KB)
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**Purpose**: Comprehensive post-getenv performance analysis
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**Contains**:
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- Q1: NEW #1 Bottleneck identification (hak_tiny_alloc 22.75%)
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- Q2: Top 5 hotspots ranking
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- Q3: Optimization worthiness assessment
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- Q4: Root cause analysis and proposed fixes
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- Before/after comparison table
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- Final recommendation with justification
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**Key Finding**: hak_tiny_alloc at 22.75% is 2.27x above 10% threshold → Optimize!
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#### OPTIMIZATION_NEXT_STEPS.md (7 KB)
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**Purpose**: Actionable implementation guide
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**Contains**:
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- Root cause breakdown from perf annotate
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- 4-phase optimization strategy (prioritized)
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- Implementation plan with time estimates
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- Success criteria and validation commands
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- Risk assessment
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- Code examples and snippets
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**Start Here**: If you're ready to implement optimizations
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#### PERF_SUMMARY.txt (2.6 KB)
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**Purpose**: Quick reference card
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**Contains**:
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- Performance journey (4 phases)
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- Optimization roadmap
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- Key metrics comparison
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- Next steps recommendation
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**Use Case**: Quick briefing or status check
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#### BOTTLENECK_COMPARISON.txt (4.4 KB)
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**Purpose**: Side-by-side before/after analysis
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**Contains**:
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- Top 10 CPU consumers comparison
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- Critical observations (4 key insights)
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- Performance trajectory visualization
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- Decision matrix (6 criteria)
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- Next bottleneck recommendation
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**Use Case**: Understanding impact of getenv fix
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---
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## Key Metrics at a Glance
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| Metric | Before (getenv bug) | After (fixed) | Change |
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|--------|---------------------|---------------|---------|
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| **Performance** | 60 M ops/sec | 120-164 M ops/sec | +86-173% |
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| **vs glibc** | -43% slower | +15-57% faster | HUGE WIN |
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| **Top bottleneck** | getenv 43.96% | hak_tiny_alloc 22.75% | Different |
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| **Allocator CPU** | ~69% | ~51% | -18% |
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| **Wasted CPU** | 44% (getenv) | 0% | -44% |
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---
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## Top 5 Current Bottlenecks
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| Rank | Function | CPU (Self) | Status | Action |
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|------|----------|-----------|---------|--------|
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| 1 | hak_tiny_alloc | 22.75% | ⚠ HIGH | OPTIMIZE |
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| 2 | __random | 14.00% | ℹ INFO | Benchmark overhead |
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| 3 | mid_desc_lookup | 12.55% | ⚠ MED | Consider optimizing |
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| 4 | hak_tiny_owner_slab | 9.09% | ✓ OK | Below threshold |
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| 5 | hak_free_at | 11.08% | ℹ INFO | Children time |
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**Primary Target**: hak_tiny_alloc (22.75%) - 2.27x above 10% threshold
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---
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## Optimization Roadmap
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### Phase 7.2.5: Eliminate getenv ✓ COMPLETE
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- **Status**: Done
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- **Impact**: -43.96% CPU, +86-173% throughput
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- **Achievement**: 60 → 120-164 M ops/sec
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### Phase 7.2.6: Optimize hak_tiny_alloc ← NEXT
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- **Target**: 22.75% → ~10% CPU
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- **Method**: Inline fast path, reduce stack, cache TLS
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- **Expected**: +50-70% throughput (→ 180-220 M ops/sec)
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- **Effort**: 2-4 hours
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### Phase 7.2.7: Optimize mid_desc_lookup (Optional)
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- **Target**: 12.55% → ~6% CPU
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- **Method**: Smaller hash table, prefetching
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- **Expected**: +10-20% additional throughput
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- **Effort**: 1-2 hours
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### Phase 7.2.8: Ship It!
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- **Condition**: All bottlenecks <10%
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- **Expected Performance**: 200-250 M ops/sec (2-3x glibc)
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- **Status**: Enable g_wrap_tiny_enabled = 1 by default
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---
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## Root Cause: hak_tiny_alloc (22.75% CPU)
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### Hotspot Breakdown
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1. **Heavy stack usage** (10.5% CPU)
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- 88 bytes allocated
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- Multiple stack reads/writes
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- Register spilling
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2. **Repeated global reads** (7.2% CPU)
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- g_tiny_initialized (3.52%)
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- g_wrap_tiny_enabled (0.28%)
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- Should cache in TLS
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3. **Complex control flow** (5.0% CPU)
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- Size validation branches
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- Magazine refill in main path
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- Should separate fast/slow paths
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### Hottest Instructions (from perf annotate)
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```asm
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3.71%: push %r14 ← Register pressure
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3.52%: mov g_tiny_initialized,%r14d ← Global read
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3.53%: mov 0x1c(%rsp),%ebp ← Stack read
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3.33%: cmpq $0x80,0x10(%rsp) ← Size check
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3.06%: mov %rbp,0x38(%rsp) ← Stack write
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```
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---
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## Proposed Solution
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### 1. Inline Fast Path (Priority: HIGH)
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**Impact**: -5 to -7% CPU
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**Effort**: 2-3 hours
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Create inline `hak_tiny_alloc_fast()`:
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- Quick size validation
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- Direct TLS magazine access
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- Fast path for magazine hit (common case)
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- Delegate to slow path only for refill
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### 2. Reduce Stack Usage (Priority: MEDIUM)
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**Impact**: -3 to -4% CPU
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**Effort**: 1-2 hours
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Reduce from 88 → <32 bytes:
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- Fewer local variables
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- Pass in registers where possible
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- Move rarely-used locals to slow path
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### 3. Cache Globals in TLS (Priority: LOW)
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**Impact**: -2 to -3% CPU
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**Effort**: 1 hour
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Cache g_tiny_initialized and g_wrap_tiny_enabled in TLS:
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- Read once on TLS init
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- Avoid repeated global reads (3.8% CPU saved)
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**Total Expected**: -10 to -15% CPU reduction (22.75% → ~10%)
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---
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## Success Criteria
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After optimization, verify:
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- [ ] hak_tiny_alloc CPU: 22.75% → <12%
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- [ ] Total throughput: 120-164 M → 180-250 M ops/sec
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- [ ] Faster than glibc: +70% to +140% (vs current +15-57%)
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- [ ] No correctness regressions
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- [ ] No new bottleneck >15%
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---
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## Files to Review/Modify
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### Source Code
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- `/home/tomoaki/git/hakmem/hakmem_pool.c` - Main implementation
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- `/home/tomoaki/git/hakmem/hakmem_pool.h` - Add inline fast path
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### Performance Data
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- `/home/tomoaki/git/hakmem/perf_post_getenv.data` - Current perf recording
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- `/home/tomoaki/git/hakmem/perf_post_getenv_annotate.txt` - Assembly hotspots
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### Benchmarks
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- `/home/tomoaki/git/hakmem/bench_comprehensive_hakmem` - Test binary
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- Run with: `HAKMEM_WRAP_TINY=1 ./bench_comprehensive_hakmem`
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---
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## Timeline
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### Completed (Today)
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- [x] Collect fresh perf data post-getenv fix
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- [x] Identify new #1 bottleneck (hak_tiny_alloc)
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- [x] Analyze root causes via perf annotate
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- [x] Compare before/after getenv fix
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- [x] Make optimization recommendation
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- [x] Create implementation guide
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### Next Session (2-4 hours)
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- [ ] Implement inline fast path
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- [ ] Reduce stack usage
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- [ ] Benchmark and validate
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- [ ] Collect new perf data
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- [ ] Assess if further optimization needed
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### Future (Optional, 1-2 hours)
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- [ ] Optimize mid_desc_lookup (12.55%)
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- [ ] Final validation
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- [ ] Enable tiny pool by default
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- [ ] Ship it!
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---
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## Questions?
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**Q: Should we stop optimizing and ship now?**
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A: No. hak_tiny_alloc at 22.75% is 2.27x above threshold. Clear optimization opportunity with high ROI (50-70% gain for 2-4 hours work).
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**Q: What if optimization doesn't work?**
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A: Low risk. We can always revert. Current performance (120-164 M ops/sec) already beats glibc, so we're not making it worse.
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**Q: How do we know when to stop?**
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A: When top bottleneck falls below 10%, or when effort exceeds returns. Currently at 22.75%, so not there yet.
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**Q: What about the other bottlenecks?**
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A: mid_desc_lookup (12.55%) is secondary target if time permits. hak_tiny_owner_slab (9.09%) is below 10% threshold and acceptable.
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---
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## Additional Resources
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### Previous Analysis (For Context)
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- `PERF_ANALYSIS_RESULTS.md` - Original analysis that identified getenv bug
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- `perf_report.txt` - Old data (with getenv bug)
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- `perf_annotate_*.txt` - Old annotations
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### Benchmark Results
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See PERF_POST_GETENV_ANALYSIS.md section "Supporting Data" for:
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- Per-test throughput breakdown
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- Size class performance (16B, 32B, 64B, 128B)
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- Comparison with glibc baseline
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---
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## Contact
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**Project**: HAKMEM Memory Allocator
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**Repository**: /home/tomoaki/git/hakmem
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**Analysis Date**: 2025-10-26
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**Analyst**: Claude Code (Anthropic)
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---
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**Last Updated**: 2025-10-26 09:08 JST
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**Status**: Ready for Phase 7.2.6 Implementation
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