ARM性能计数器vs linux clock_gettime

I am using a Zynq chip on a development board ( ZC702 ) , which has a dual cortex-A9 MPCore at 667MHz and comes with a Linux kernel 3.3 I wanted to compare the execution time of a program so first a used clock_gettime and then used the counters provided by the co-processor of ARM. The counter increment every one processor cycle. ( based on this I am using a Zynq chip on a development board (