[G1-Sync] Manual knowledge update

10_Wiki/Topics/DevOps_and_Security/CPU Bottleneck.md

@@ -2,21 +2,157 @@
 id: wiki-2026-0508-cpu-bottleneck
 title: CPU Bottleneck
 category: 10_Wiki/Topics
-status: merged
-redirect_to: 성능_프로파일링_및_메모리_관리_표준
-canonical_id: wiki-2026-0508-040
-aliases: []
+status: verified
+canonical_id: self
+aliases: [CPU-Bound, Compute Bottleneck]
 duplicate_of: none
 source_trust_level: A
-confidence_score: 0.92
-tags: [uncategorized]
+confidence_score: 0.9
+verification_status: applied
+tags: [performance, profiling, cpu]
 raw_sources: []
-last_reinforced: 2026-05-08
-github_commit: pending
-inferred_by: Claude Opus 4.7 (auto-normalize 2026-05-08)
+last_reinforced: 2026-05-10
+github_commit: applied
+tech_stack:
+  language: C++/Rust/JS
+  framework: perf/Instruments/Chrome DevTools
 ---
 
-# Redirect
+# CPU Bottleneck
 
-이 문서는 Canonical 문서인 [[성능_프로파일링_및_메모리_관리_표준]]으로 통합되었습니다.
-모든 최신 지식과 세부 내용은 위 링크를 참조하십시오.
+## 매 한 줄
+> **"매 GPU 가 놀고 main thread 가 100% 면 CPU bottleneck."**. CPU bottleneck 은 frame budget 16.7ms (60fps) 또는 11ms (90fps XR) 안에 main thread 작업이 안 끝나는 상태. 2026 진단: Chrome Performance panel + perf + Instruments → fix: WebWorker / WASM SIMD / off-main-thread / batching.
+
+## 매 핵심
+
+### 매 진단 신호
+- GPU utilization < 70% but FPS drop.
+- Long Task > 50ms in Performance panel.
+- `perf top` 의 single function 이 hot.
+- Profile 의 self-time 이 한 함수에 집중.
+
+### 매 Bottleneck Source
+- **Main-thread JS**: parse, layout, large loop.
+- **Layout thrash**: read-write-read DOM.
+- **GC pause**: allocation pressure.
+- **Synchronous IO**: blocking syscall.
+- **Unoptimized algorithm**: O(n²) on hot path.
+- **Single-core saturation**: no parallelism.
+
+### 매 Fix Strategy
+1. **Profile first** — 매 measure, not guess.
+2. **Off-main-thread**: WebWorker, OffscreenCanvas.
+3. **Batch**: requestAnimationFrame, microtask.
+4. **SIMD/WASM**: 매 hot inner loop.
+5. **Algorithmic**: O(n²) → O(n log n).
+6. **Cache**: memoize, weak-ref.
+7. **Lazy**: defer, code-split.
+
+## 💻 패턴
+
+### Detect long task
+```javascript
+const obs = new PerformanceObserver(list => {
+  for (const e of list.getEntries()) {
+    if (e.duration > 50) console.warn('long task', e.duration, e.name);
+  }
+});
+obs.observe({ entryTypes: ['longtask'] });
+```
+
+### Move work to Worker
+```javascript
+// main.js
+const w = new Worker('worker.js', { type: 'module' });
+w.postMessage({ data: bigArray }, [bigArray.buffer]); // 매 transfer, zero-copy
+w.onmessage = e => render(e.data);
+
+// worker.js
+self.onmessage = e => {
+  const result = heavyCompute(e.data.data);
+  self.postMessage(result, [result.buffer]);
+};
+```
+
+### WASM SIMD hot loop (Rust)
+```rust
+#[target_feature(enable = "simd128")]
+unsafe fn dot_product(a: &[f32], b: &[f32]) -> f32 {
+    use std::arch::wasm32::*;
+    let mut sum = f32x4_splat(0.0);
+    for i in (0..a.len()).step_by(4) {
+        let va = v128_load(a.as_ptr().add(i) as *const v128);
+        let vb = v128_load(b.as_ptr().add(i) as *const v128);
+        sum = f32x4_add(sum, f32x4_mul(va, vb));
+    }
+    f32x4_extract_lane::<0>(sum) + f32x4_extract_lane::<1>(sum)
+      + f32x4_extract_lane::<2>(sum) + f32x4_extract_lane::<3>(sum)
+}
+```
+
+### Time-sliced loop (yield to event loop)
+```javascript
+async function processChunked(items) {
+  const CHUNK = 200;
+  for (let i = 0; i < items.length; i += CHUNK) {
+    items.slice(i, i + CHUNK).forEach(processOne);
+    await new Promise(r => setTimeout(r, 0));   // 매 yield
+  }
+}
+// 또는 scheduler.yield() (2025+)
+if ('scheduler' in window && 'yield' in scheduler) await scheduler.yield();
+```
+
+### Batch DOM read/write
+```javascript
+// 매 안티 — layout thrash
+items.forEach(el => { const w = el.offsetWidth; el.style.width = (w*2)+'px'; });
+// 매 fix — read first, then write
+const widths = items.map(el => el.offsetWidth);
+items.forEach((el, i) => { el.style.width = (widths[i]*2)+'px'; });
+```
+
+### Linux perf hot function
+```bash
+sudo perf record -F 99 -g -p $(pidof myapp) -- sleep 10
+sudo perf report --stdio | head -40
+sudo perf script | stackcollapse-perf.pl | flamegraph.pl > flame.svg
+```
+
+## 매 결정 기준
+| 상황 | Approach |
+|---|---|
+| Long JS function | WebWorker / time-slice |
+| Image/video pipeline | OffscreenCanvas |
+| Number crunching | WASM SIMD / GPU compute |
+| Layout thrash | read-then-write batch |
+| GC pressure | object pool |
+| Multi-core unused | Worker pool / parallel |
+
+**기본값**: 매 measure → identify hot fn → off-main-thread or algorithmic fix.
+
+## 🔗 Graph
+- 부모: [[Analyze runtime performance]] · [[Flame_Graphs]]
+- 변형: [[Draw Call]]
+- 응용: [[Tree Shaking (번들 크기 최적화)]] · [[Frustum Culling]]
+- Adjacent: [[Memory Management]] · [[Branch Prediction]]
+
+## 🤖 LLM 활용
+**언제**: profile flamegraph 해석, hot-function refactor 제안, perf annotation.
+**언제 X**: 매 actual perf measurement — deterministic 도구가 정확.
+
+## ❌ 안티패턴
+- **Premature optimization**: 매 profile 없이 추측 — 잘못된 부분 fix.
+- **Worker overuse**: 매 small task 의 postMessage 오버헤드 > 이득.
+- **`while(true)` busy-wait**: 매 throttle / requestIdleCallback 사용.
+- **Synchronous XHR**: 매 deprecated, main-thread block.
+
+## 🧪 검증 / 중복
+- Verified: Chrome Performance docs; web.dev Long Tasks; Linux perf-tools (Brendan Gregg).
+- 신뢰도 A.
+
+## 🕓 Changelog
+| 날짜 | 변경 |
+|---|---|
+| 2026-05-08 | Phase 1 |
+| 2026-05-10 | Manual cleanup — diagnosis + Worker/SIMD/yield patterns |