perf stat frontend and backend cycles showing greater than 100%

Question

I'm trying to benchmark a piece of code written in C using perf and I get over 100% in the frontend idle cycles count. I've seen this happen for the backend idle cycles count as well. Both over 100 at the same time. The number of instructions per cycle is a pretty high amount - ranging from 5 - 10.

3,569,966 stalled-cycles-frontend   #  111.98% frontend cycles idle   
1,843,327 stalled-cycles-backend    #   57.82% backend  cycles idle   
17,875,020 instructions             #    5.61  insns per cycle        
                                    #    0.20  stalled cycles per insn

What does it mean when the percent is so high?

Answer 1

These percentages are with respect to active CPU cycles, which is displayed as cycles. So, cycles is not the total cycles but the active CPU cycles, and front-end or back-end stalled cycles are computed with respect to it.