The importance of having a good branch predictor depends on how often conditional branches  are executed. Together with branch predictor accuracy, this will determine how much time is  spent stalling due to mispredicted branches. In this exercise, assume that the breakdown of  dynamic instructions into various instruction categories is as follows:  Also, assume the following branch predictor accuracies:  Stall cycles due to mispredicted branches increase the CPI. What is the extra CPI due to  mispredicted branches with the always-taken predictor? Assume that branch outcomes  are determined in the EX stage, that there are no data hazards, and that no delay slots  are used.  b. With the 2-bit predictor, what speedup would be achieved if we could convert half of  the branch instructions in a way that replaces a branch instruction with an ALU instruction? Assume that correctly and incorrectly predicted instructions have the same  chance of being replaced.

Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
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The importance of having a good branch predictor depends on how often conditional branches  are executed. Together with branch predictor accuracy, this will determine how much time is  spent stalling due to mispredicted branches. In this exercise, assume that the breakdown of  dynamic instructions into various instruction categories is as follows: 

Also, assume the following branch predictor accuracies: 

  1. Stall cycles due to mispredicted branches increase the CPI. What is the extra CPI due to  mispredicted branches with the always-taken predictor? Assume that branch outcomes  are determined in the EX stage, that there are no data hazards, and that no delay slots  are used. 

b. With the 2-bit predictor, what speedup would be achieved if we could convert half of  the branch instructions in a way that replaces a branch instruction with an ALU instruction? Assume that correctly and incorrectly predicted instructions have the same  chance of being replaced.

R-Type
BEQ
JMP
LW
SW
40%
25%
5%
25%
5%
Also, assume the following branch predictor accuracies:
Always-Taken
Always-Not-Taken
2-Bit
45%
55%
85%
Transcribed Image Text:R-Type BEQ JMP LW SW 40% 25% 5% 25% 5% Also, assume the following branch predictor accuracies: Always-Taken Always-Not-Taken 2-Bit 45% 55% 85%
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