luokai0 Computer Architecture Expert
Before Starting
- RISC or CISC architecture?
- Single-core performance or parallel throughput?
- Hardware design or software optimization focus?
Core Expertise Areas
Instruction Set Architecture
RISC: few simple instructions, load-store, uniform format, many registers. CISC: many complex instructions, memory operands, variable length, fewer registers. RISC-V: open standard ISA, modular extensions, growing adoption. ARM: dominant in mobile and embedded, energy efficient, RISC-based. x86-64: dominant in servers and desktop, CISC with RISC-like microops internally.
CPU Pipeline
Classic 5-stage: fetch, decode, execute, memory, writeback. Pipeline hazards: structural (resource conflict), data (RAW/WAW/WAR), control (branches). Hazard solutions: stalling, forwarding, branch prediction, out-of-order execution. Superscalar: multiple execution units, issue multiple instructions per cycle. Out-of-order execution: Tomasulo algorithm, reorder buffer, register renaming.
Cache Hierarchy
L1/L2/L3: smaller and faster closer to CPU, larger and slower further. Cache mapping: direct-mapped, set-associative, fully associative. Replacement: LRU, pseudo-LRU, random. Write policy: write-through vs write-back, write-allocate vs no-write-allocate. Cache coherence: MESI protocol for multi-core systems.
Memory Systems
DRAM: row and column access, refresh cycles, banks and ranks. Memory hierarchy: registers, L1, L2, L3, DRAM, SSD, HDD — latency increases. Virtual memory: TLB, page tables, huge pages for performance. NUMA: non-uniform memory access in multi-socket systems.
GPU Architecture
SIMT: single instruction multiple threads, thousands of lightweight threads. Streaming multiprocessors: groups of CUDA cores sharing instruction unit. Memory hierarchy: registers, shared memory, L1, L2, global memory (DRAM). Warp divergence: different control flow paths stall efficiency.
Best Practices
- Profile before optimizing — measure actual bottleneck
- Optimize for cache locality — access memory sequentially
- Avoid branch mispredictions in hot paths
- Use SIMD intrinsics for data-parallel operations
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Cache thrashing | Improve spatial and temporal locality |
| False sharing | Align concurrent data to separate cache lines |
| Branch misprediction in tight loops | Profile and restructure to help predictor |
| Memory bandwidth saturation | Reduce data movement, use compression |
Related Skills
- operating-systems-expert
- embedded-expert
- linux-expert