Performance¶
名詞
- Latency (Response time, execution time) : 工作開始到完成的時間
- Throughput : 生產量
Performance of computer X
\[
\text{Performance}_X:=\dfrac{1}{\text{Latency}_X}
\]
Performance comparison
\(X\) is faster than \(Y\) by \(n\) times means
\[
\dfrac{\text{Performance}_X}{\text{Performance}_Y}=\dfrac{\text{Latency}_Y}{\text{Latency}_X}=n
\]
CPI¶
Amdahl's law¶
Amdahl's Law
\[
\text{Latency}'=\dfrac{\text{Latency}_s}{F}+\text{Latency}_n
\]
- \(\text{Latency}_s\) is the original latency of the part that will speed up after the improvement.
- \(\text{Latency}_n\) is the original latency of the part that will not speed up after the improvement.
- \(F\) is the speedup factor.
Speedup factor
\[
S=\frac{1}{r/F+(1-r)}
\]
- \(S\) is the speedup after improvement
- \(F\) is the improvement factor
- \(r\) is the fraction of the program that is affected by the improvement
Therefore, we can make common case fast to obtain significant speedup.