c - Using clock() to measure execution time

Question

I am running a C program using GCC and a proprietary DSP cross-compiler to simulate some functioality. I am using the following code to measure the execution time of particular part of my program:

clock_t start,end;
printf("DECODING DATA:
");
start=clock();
conv3_dec(encoded, decoded,3*length,0);
end=clock();
duration = (double)(end - start) / CLOCKS_PER_SEC;
printf("DECODING TIME = %f
",duration);

where conv3_dec() is a function defined in my program and I want to find the run-time of this function.

Now the thing is when my program runs, the conv3_dec() functions runs for almost 2 hours but the output from the printf("DECODING TIME = %f ",duration) says that the execution of the function finished in just half a second (DECODING TIME = 0.455443) . This is very confusing for me.

I have used the clock_t technique to measure the runtimes of programs previously but the difference has never been so huge. Is this being caused by the cross-compiler. Just as a side note, the simulator simulates a DSP processor running at just 500MHz, so is the difference in the clock speeds of the DSP processor and my CPU causing the error is measuring the CLOCKS_PER_SEC.

Answer 1

clock measures the cpu time and not the wallclock time. Since you are not running the majority of your code on the cpu, this is not the right tool.