1. Out-of-Order Execution (OoOE)
CPU Optimization
Out-of-Order Execution (OoOE)

2. Stalling a Checkout Line Ever forgot to get a barcode?

3. ALU CPU with separate instruction and data caches FLASH RAM
Instruction Cache
Data Cache
ALU

4. Pipeline with instruction & data cache
An Ideal Pipeline
Pipeline with instruction & data cache
Instruction NOT in cache
Operand NOT in cache

5. Example: How long would this program take to execute?
R1 = R2 R2 = R1 + R3 R4 = R3 + R5
*R3, R4, R5 Already in data cache

6. R1=R2 F D A E W R2=R1+R3 R4=R3+R5 R4=R3+R5 F E A W R1=R2 D R2=R1+R3
Sequential Execution
R1=R2 F D A E W
R2=R1+R3
R4=R3+R5
Time = 12 Units
Re-ordered Execution
R4=R3+R5 F E A W
R1=R2 D
R2=R1+R3
Time = 12 Units

7. The CDC 6600. The first computer to use OoOE (1964)
Source: wikipedia

8. Reservation Stations (Buffer)
R1=R2
RAM
R2=R1+R3
cache
R4=R3+R5

9. OoOE Hardware