Performance

• Response Time :

How long it takes to do a task

• Throughput :

Total work done per unit time

• Definition of Performance :

Performance = 1 / Execution Time

If X is n time faster than Y, Performance(x) / Performance(y) = n

Execution Time :

1.Elapsed time :

Total response time

Determines system performance

Ex: time sharing ---->太快感覺不出來

★ 2.CPU time: (通常用這個比較)

Time spent processing a given job

CPU Time :

CPU Time = CPU Clock Cycles * Clock Cycle Time

= CPU Clock Cycles / Clock frequency

又

Clock Cycles = Instruction Count (Ci) * Cycles per Instruction (CPI)

CPI : 一個 instruction 有幾個 Cycle

因此，

CPU Time = Ci * CPI * Clock Cycle Time

= Ci * CPI / Clock frequency

Ci 影響因素:

----> program, instruction set architecture (ISA 指令集架構) and compiler

CPI影響因素:

-----> ISA，different instructions have different CPI

因此， 要比較就要在Same ISA 下~~~~

★★★ If different instruction classes take different numbers of cycles.....

--> 每個狀況都加總起來

因此，