Concept of clock tick and clock cycles

问题

I have written a very small code to measure the time taken by my multiplication algorithm :

  clock_t begin, end;
  float time_spent;

begin = clock();
a = b*c;
end = clock();
time_spent = (float)(end - begin)/CLOCKS_PER_SEC;

I am working with mingw under Windows.

I am guessing that end = clock() will give me the clock ticks at that particular moment. Subtracting it from begin will give me clock ticks consumed by multiplication. When I divide with CLOCKS_PER_SEC, I will get the total amount of time.

My first question is: Is there a difference between clock ticks and clock cycle?

My algorithm here is so small that the difference end-begin is 0. Does this mean that my code execution time was less than 1 tick and that's why I am getting zero?

回答1:

four your first question: clock ticks refer to the main system clock. It is the smallest unit of time recognized by the device. clock cycle is the time taken for a full processor pulse to complete. this u can recognize by your cpu cpeed given in Hz. a 2GHz processor performs 2,000,000,000 clock cycles per second.

for your second question: probably yes.

回答2:

My first question is: Is there a difference between clock ticks and clock cycle?

Yes. A clock tick could be 1 millisecond or microsecond while the clock cycle could be 0.3 nanoseconds. On POSIX systems CLOCKS_PER_SEC must be defined as 1000000 (1 million). Note that if the CPU measurement cannot be obtained with microsecond resolution then the smallest jump in the return value from clock() will be larger than one.

My algorithm here is so small that the difference end-begin is 0. Does this mean that my code execution time was less than 1 tick and that's why I am getting zero?

Yes. To get a better reading I suggest that you loop enough iterations so that you measure over several seconds.

回答3:

A clock cycle is a clock tick.

A clock cycle is the speed of a computer processor, or CPU, and is determined by the amount of time between two pulses of an oscillator. Generally speaking, the higher number of pulses per second, the faster the computer processor will be able to process information.

来源：https://stackoverflow.com/questions/25743995/concept-of-clock-tick-and-clock-cycles

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