Lec 2 Performance

Response Time and Throughput

• Response time (also called execution
  time)
  • How long it takes to do a task
• Throughput
  • Total work done per unit time
  • e.g., tasks/transactions/… per hour
    

Realative Performance

x,y 분자 분모 뒤바뀌는거 주의
x가 n만큼 y보다 빠르다 or 느리다

Measuring Execution Time

• Elapsed time ( total excution time, wall time)
  - Total response time, Including all aspects

  • $ time ls: measure time under the file, ls(list files in derectory)

• CPU Time
  - Time spent processing a given job

CPU Time

거속시 관계처럼 유연하게 생각하기

Perfomance improved by

• reducing number of clock cycle
• increasing clock rate

Example

Computer A: 2GHz clock, 10s CPU time
• Designing Computer B
– Aim for 6s CPU time
– Can do faster clock, but causes 1.2 × clock cycles

• How fast must Computer B clock be?

CPI (Cycle per Insturction)

Instruction Count for a program

• Determined by program, ISA and compiler

ISA (instruction set Architecture)

• defines types of instuctions

• defines addressing mode

  	ALU: ADD R1, R2, R3 -> Register addressing mode
  	BNE R1, R2, L1
  	LD R, 8(R2) -> Indirect addressing mode

bracket means no data -> need to access memory

RISC (Reduced Inst Set Computing)

• ADD R1 R2 R3: add R2, R3

CISC (Complex Inst Set Computing)

• ADD R1, (R2), (R3): bring R2, R3 data from memory and add -> store to R1
• include multiple instructions
• inefficient

 j = b(i) + c(i)
 
 RISC - MIPS, ARM
 LD R4, (R2)
 LD R5, (R3)
 ADD R1, R4, R5
 
 CISC
 ADD R1, (R2), (R3)

Average cycles per instruction

• Determined by CPU hardware
• If different instructions have different CPI