Mastering Linux Kernel Development

Calculating elapsed time

Until this point we know that in every system there is a free-running, ever-incrementing counter, and all time is derived from it, be it wall time or any duration. The most natural idea here to calculate the time (seconds elapsed since the start of counter) would be dividing the number of cycles provided by this counter with the clock frequency, as expressed in the following formula:

Time (seconds) = (counter value)/(clock frequency)

There is a catch with this approach, however: it involves division (which works on an iterative algorithm, making it the slowest among the four basic arithmetic operations) and floating point calculations, which might be slower on certain architectures. While working with embedded platforms, ...