178 lines
4.9 KiB
Markdown
178 lines
4.9 KiB
Markdown
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# TLS Layout Analysis (Phase v11b-1 Current State)
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## Overview
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現在の ULTRA TLS は **クラス別に独立した struct** が散在しており、L1D キャッシュ効率が悪い。
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## TLS Structures (ULTRA C4-C7)
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### 1. TinyC7UltraFreeTLS (`tiny_c7_ultra_tls_t`)
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```c
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typedef struct tiny_c7_ultra_tls_t {
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uint16_t count; // 2B (hot)
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uint16_t _pad; // 2B
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void* freelist[128]; // 1024B (128 * 8)
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// --- cold fields ---
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uintptr_t seg_base; // 8B
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uintptr_t seg_end; // 8B
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tiny_c7_ultra_segment_t* seg; // 8B
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void* page_base; // 8B
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size_t block_size; // 8B
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uint32_t page_idx; // 4B
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tiny_c7_ultra_page_meta_t* page_meta; // 8B
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bool headers_initialized; // 1B
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} tiny_c7_ultra_tls_t;
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```
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| Field | Size | Total |
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|-------|------|-------|
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| Hot (count + freelist) | 4 + 1024 | 1028B |
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| Cold (seg_base...headers_initialized) | ~53B | ~53B |
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| **Total** | | **~1080B (17 cache lines)** |
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### 2. TinyC6UltraFreeTLS
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```c
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typedef struct TinyC6UltraFreeTLS {
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void* freelist[128]; // 1024B (128 * 8)
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uint8_t count; // 1B
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uint8_t _pad[7]; // 7B
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uintptr_t seg_base; // 8B
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uintptr_t seg_end; // 8B
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} TinyC6UltraFreeTLS;
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```
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| Field | Size |
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|-------|------|
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| freelist | 1024B |
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| count + pad | 8B |
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| seg_base/end | 16B |
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| **Total** | **1048B (17 cache lines)** |
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### 3. TinyC5UltraFreeTLS
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Same as C6: **1048B (17 cache lines)**
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### 4. TinyC4UltraFreeTLS
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```c
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typedef struct TinyC4UltraFreeTLS {
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void* freelist[64]; // 512B (64 * 8)
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uint8_t count; // 1B
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uint8_t _pad[7]; // 7B
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uintptr_t seg_base; // 8B
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uintptr_t seg_end; // 8B
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} TinyC4UltraFreeTLS;
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```
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| Field | Size |
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|-------|------|
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| freelist | 512B |
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| count + pad | 8B |
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| seg_base/end | 16B |
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| **Total** | **536B (9 cache lines)** |
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### 5. SmallMidV35TlsCtx (MID v3.5)
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```c
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typedef struct {
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void *page[8]; // 64B
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uint32_t offset[8]; // 32B
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uint32_t capacity[8]; // 32B
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SmallPageMeta_MID_v3 *meta[8]; // 64B
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} SmallMidV35TlsCtx;
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```
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| Field | Size |
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|-------|------|
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| page[8] | 64B |
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| offset[8] | 32B |
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| capacity[8] | 32B |
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| meta[8] | 64B |
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| **Total** | **192B (3 cache lines)** |
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## Summary: Total TLS Footprint
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| Structure | Size | Cache Lines |
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|-----------|------|-------------|
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| TinyC7UltraFreeTLS | 1080B | 17 |
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| TinyC6UltraFreeTLS | 1048B | 17 |
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| TinyC5UltraFreeTLS | 1048B | 17 |
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| TinyC4UltraFreeTLS | 536B | 9 |
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| SmallMidV35TlsCtx | 192B | 3 |
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| **Total ULTRA (C4-C7)** | **3712B** | **~60 lines** |
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## Problem Analysis
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### 1. Hot Path に必要な最小フィールド
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| Operation | Required Fields |
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|-----------|-----------------|
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| alloc (TLS hit) | count, freelist[count-1] |
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| free (TLS push) | count, freelist[count], seg_base/end |
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**Hot path は実質 count + head + seg_range の ~24B で済む。**
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### 2. 現状の問題
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1. **freelist 配列が巨大**: 各クラス 512-1024B の配列を TLS に保持
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2. **クラス間で seg_base/end が重複**: C4-C7 が同一セグメント範囲なら共有可能
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3. **count の配置が非統一**: C7 は先頭、C4-C6 は freelist の後ろ
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4. **Cold fields が hot 領域に混在**: C7 の page_meta 等が毎回ロード
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### 3. Cache Miss の原因
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- alloc/free のたびに **各クラス専用の TLS struct** をアクセス
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- 4 クラス × 平均 16 cache lines = **64 cache lines が L1D を争奪**
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- Mixed workload では C4-C7 がランダムに切り替わり、thrashing 発生
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---
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## Phase TLS-UNIFY-2a: C4-C6 Unified TLS (2025-12-12)
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### 実装内容
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C4-C6 ULTRA の TLS を `TinyUltraTlsCtx` 1箱に統合:
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```c
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typedef struct TinyUltraTlsCtx {
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// Hot line: counts (8B aligned)
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uint16_t c4_count;
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uint16_t c5_count;
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uint16_t c6_count;
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uint16_t _pad_count;
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// Per-class segment ranges (learned on first free)
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uintptr_t c4_seg_base, c4_seg_end;
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uintptr_t c5_seg_base, c5_seg_end;
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uintptr_t c6_seg_base, c6_seg_end;
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// Per-class array magazines
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void* c4_freelist[64]; // 512B
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void* c5_freelist[64]; // 512B
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void* c6_freelist[128]; // 1024B
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} TinyUltraTlsCtx;
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// Total: ~2KB per thread
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```
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**変更点**:
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- C4/C5/C6 の TLS を 1 struct に統合
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- 配列マガジン方式を維持（安全）
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- C7 は別箱のまま（既に安定）
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- 旧 `TinyC4/5/6UltraFreeTLS` への委譲を廃止
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### A/B テスト結果
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| Test | v11b-1 (Phase 1) | TLS-UNIFY-2a | Diff |
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|------|------------------|--------------|------|
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| Mixed 16-1024B | 8.0-8.8 Mop/s | 8.5-9.0 Mop/s | +0~5% |
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| MID 257-768B | 8.5-9.0 Mop/s | 8.1-9.0 Mop/s | ±0% |
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**結果**: 性能同等以上、SEGV/assert なし ✅
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---
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**Date**: 2025-12-12
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**Phase**: TLS-UNIFY-2a completed
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