exp8: 单机性能优化
Less than 1 minuteAbout 278 words
Task 0
Performance
| Option | Elapsed Time / seconds | Performance / GFlops |
|---|---|---|
-O0 | 1.0072 | 0.2665 |
-O1 | 0.3461 | 0.7755 |
-O2 | 0.3332 | 0.8057 |
-O3 | 0.0496 | 5.4081 |
-fast | 0.0386 | 6.9524 |
Task 1
Performance
UNROLL_N | Elapsed Time / seconds | Performance / GFlops |
|---|---|---|
| 1 | 2.0814 | 15.7431 |
| 2 | 1.9311 | 16.9688 |
| 4 | 1.8048 | 18.1562 |
| 8 | 1.7787 | 18.4227 |
| 16 | 1.8276 | 17.9297 |
回答问题
Question 1
请参考 ICC 手册 并简述参数 (-O0, -O1, -O2, -O3, -fast) 分别进行了哪些编译优化。每种参数罗列几个优化技术即可。
Answer 1
-O0
禁用所有优化
-O1
- data-flow analysis
- code motion
- strength reduction and test replacement
- split-lifetime analysis
- instruction scheduling
-O2
- Vectorization
- Inlining of intrinsics
- inlining
- constant propagation
- forward substitution
- routine attribute propagation
- variable address-taken analysis
- dead static function elimination
- removal of unreferenced variables
-O3
- Fusion
- Block-Unroll-and-Jam
- collapsing
ifstatements
-fast
- interprocedural optimization between files
- optimization of floating-point divides that give slightly less precise results than full IEEE division
- link all libraries statically
- generate instructions for the highest instruction set available
Question 2
请简述任务一中循环展开带来的好处。
Answer 2
- 可以减少循环变量的比较次数和分支跳转次数
- 减少数据依赖, 增加并发, 充分利用 CPU 流水线