使い方
- インストールコマンドをコピーし、自分の環境へ導入する前にソースを確認します。
- 必要なツール、認証情報、対応環境を原文で確認します。
- 入力と成果物を指定し、出力を資料と照合します。
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill cpu-pipelines-and-hazards開始前の確認
- 導入にはモデル契約、API枠、ファイルへのアクセス許可は含まれません。
- スター数や導入数は活動の指標であり、独立した品質・安全性試験ではありません。
リポジトリの原文
見出し、例、コード、表、リンク、参照画像を含む原文を表示しています。
CPU Pipelines and Hazards
Purpose
Explain classic and modern CPU pipeline concepts: stages, data and control hazards, forwarding/bypassing, stalls, and branch handling — foundational for optimization and understanding microarchitecture counters.
When to Use
- Interpreting pipeline stall metrics from
skills/profilers/intel-vtune-amd-uprof - Teaching why instruction order affects throughput
- Relating assembly scheduling to hardware behavior
- Debugging unexpected performance cliffs in hot loops
Workflow
1. Five-stage classic pipeline (MIPS-style mental model)
IF → ID → EX → MEM → WBOverlapped execution: instruction N in EX while N+1 in ID.
2. Data hazards
| Type | Example | Mitigation |
|---|---|---|
| RAW (true) | add r1,r2,r3 then sub r4,r1,r5 | Forwarding from EX/MEM/WB |
| WAR / WAW | Rare in in-order; relevant in OoO rename | Register renaming |
Without forwarding:
stall until writeback completes3. Control hazards (branches)
Branch in ID → target unknown until EX
├── Predict taken/not-taken (static or dynamic)
├── Flush wrong-path instructions on mispredict
└── Penalty = pipeline depth (varies by CPU)See skills/computer-architecture/branch-prediction-and-speculation.
4. Structural hazards
Limited functional units (single memory port) cause stalls even without dependencies.
5. Practical optimization hints
c
/* Bad — tight dependency chain */
for (int i = 0; i < n; i++)
acc = acc + data[i]; /* each iter waits on acc */
/* Better — multiple accumulators (ILP) */
acc0 = acc1 = 0;
for (int i = 0; i < n; i += 2) {
acc0 += data[i];
acc1 += data[i+1];
}
acc = acc0 + acc1;Pair with skills/low-level-programming/cpu-cache-opt — memory often dominates.
6. Reading uops / ports (x86)
bash
perf stat -e instructions,cycles,stalls-frontend,stalls-backend ./appVTune "Microarchitecture Exploration" maps to pipeline slots.
7. Agent usage
/cpu-pipelines-and-hazards Explain RAW hazard in this ARM assembly loop and how to break itCommon Problems
| Symptom | Cause | Fix |
|---|---|---|
High stalls-frontend | I-cache misses / branch mispredict | Align hot loop; see branch skill |
| No speedup from unroll | Memory bound | Profile loads; prefetch |
| Wrong cycle model | Ignored OoO execution | Use perf hardware counters |
| "NOP fixes it" | Timing-sensitive MMIO | Never tune device delays by NOP |
Related Skills
skills/computer-architecture/branch-prediction-and-speculation— mispredict costskills/computer-architecture/memory-hierarchy-and-caches— load latencyskills/low-level-programming/cpu-cache-opt— cache-line effectsskills/profilers/intel-vtune-amd-uprof— pipeline analysisskills/low-level-programming/assembly-arm— instruction scheduling
