A computer with an 11stage pipeline deals with conditional b

A computer with an 11-stage pipeline deals with conditional branches by stalling

for the next 9 cycles after hitting one. How much does stalling hurt the perfor-

mance if 10 percent of all instructions are conditional branches? Ignore all sources

of stalling except conditional branches.

Solution:

Given 1 out of 5 instructions stalls, on average.

So Each stage will see, on average, 11 instructions followed by 9 idle states.

And regardless of the number of stages, this is 9/11 more cycles (81%) than the ideal where all stages are fully busy.

In terms of throughput, only 11 of every 20 cycles is useful in each stage, so this amounts to a 9/20 (45%) loss in throughput.