Example

• Determine the total branch penaltyfor branch target buffer assuming the penalty cycles for mispredictions as in Fig.4.24:. Assume prediction accuracy 90% and hit rate 90%, branch frequency 60%.

• branch penalty = penalty due (hit but not taken + miss but taken)

• = Percent Hit * Incorrect Prediction * 2 + Percent Miss * Taken Branches * 2

• = (90 * 10 * 2 + 10 * 60 * 2 )/ 100 = 0.18 + 0.12 = 0.30.

• Meaning: every branch incurs .30 cycles more time on a average. (compare this to dealyed branch : 0.50)

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