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Out-of-Order Execution (OoOE)
CPU Optimization Out-of-Order Execution (OoOE)
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Stalling a Checkout Line Ever forgot to get a barcode?
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ALU CPU with separate instruction and data caches FLASH RAM
Instruction Cache Data Cache ALU
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Pipeline with instruction & data cache
An Ideal Pipeline Pipeline with instruction & data cache Instruction NOT in cache Operand NOT in cache
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Example: How long would this program take to execute?
R1 = R2 R2 = R1 + R3 R4 = R3 + R5 *R3, R4, R5 Already in data cache
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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
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The CDC 6600. The first computer to use OoOE (1964)
Source: wikipedia
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Reservation Stations (Buffer)
R1=R2 RAM R2=R1+R3 cache R4=R3+R5
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OoOE Hardware
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