time measurement in kernel

ktime_t start_time, end_time;
s64 delay_time;

start_time = ktime_get();
udelay(10);
end_time = ktime_get();

delay_time = ktime_to_ns(end_time) - ktime_to_ns(start_time);
printk("delay_time %lld nsec\n", delay_time);