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CSCE 212 Quiz 9a – 4/1/11

CSCE 212 Quiz 9a – 4/1/11. For the following questions, assume the clock cycle times given above and the following set of instructions: lw $5, -16($5) sw $5, -16($5) add $5, $5, $5 What is the total execution time of this instruction sequence without forwarding and with full forwarding?

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CSCE 212 Quiz 9a – 4/1/11

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  1. CSCE 212 Quiz 9a – 4/1/11 For the following questions, assume the clock cycle times given above and the following set of instructions: lw $5, -16($5) sw $5, -16($5) add $5, $5, $5 • What is the total execution time of this instruction sequence without forwarding and with full forwarding? • What is the speed-up achieved by adding full forwarding to a pipeline that had no forwarding? *ALU instruction can forward a value to EX stage of next instruction.

  2. CSCE 212 Quiz 9a Answers First determine nops and total clock cycles. WithoutWith lw $5, -16($5) lw $5, -16($5) nop nop nop sw $5, -16($5) sw $5, -16($5) add $5, $5, $5 add $5, $5, $5 (7 + 2 clock cycles) (7 + 1 clock cycles)

  3. CSCE 212 Quiz 9a Answers • What is the total execution time of this instruction sequence without forwarding and with full forwarding? Without(7 + 2) x 200ps = 1800ps With (7 + 1) x 250ps = 2000ps

  4. CSCE 212 Quiz 9a Answers • What is the speed-up achieved by adding full forwarding to a pipeline that had no forwarding? 1800/2000 = 0.90 (actually a slowdown)

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