This test tries its best to report the producer side underlying futex
wake syscall overhead wthin sem_post. It does not measure the time it
takes for the wakeup to propagate to the consumer. It suffers from
clock_gettime syscall overhead, so subtract that. Lock the CPU speed
for consistent results as we may not reach >50% cpu utilization.
Change-Id: I02fa9dab2e6ac27202f0290115150bd3c8de00f2