Measuring system call execution time () in C ++

Question

I found code for measuring runtime here http://www.dreamincode.net/forums/index.php?showtopic=24685

However, it does not work for calls in system (). I suppose this is because execution jumps out of the current process.

clock_t begin=clock(); system(something); clock_t end=clock(); cout<<"Execution time: "<<diffclock(end,begin)<<" s."<<endl; 

Then

 double diffclock(clock_t clock1,clock_t clock2) { double diffticks=clock1-clock2; double diffms=(diffticks)/(CLOCKS_PER_SEC); return diffms; } 

However, this always returns 0 seconds ... Is there any other way that will work?

It is also on Linux.

Edit: also, to add, the runtime is of the order of an hour. Therefore, accuracy is not a problem.

Thanks!

Answer 1

Do you find using gettimeofday ?

 struct timeval tv; struct timeval start_tv; gettimeofday(&start_tv, NULL); system(something); double elapsed = 0.0; gettimeofday(&tv, NULL); elapsed = (tv.tv_sec - start_tv.tv_sec) + (tv.tv_usec - start_tv.tv_usec) / 1000000.0; 

Answer 2

Unfortunately, clock () has only one second resolution on Linux (although it returns time in units of microseconds).

Many people use gettimeofday () for benchmarking, but this means that elapsed time - not the time used by this process / thread - is not ideal. Obviously, if your system is more or less idle, and your tests are quite long, you can average the results. Usually less of a problem, but it's worth knowing that the time returned by gettimeofday () is non-monotonous - it can jump a bit, for example. when your system first connects to an NTP time server.

The best thing for benchmarking is clock_gettime () with whatever option is most suitable for your task.

• CLOCK_THREAD_CPUTIME_ID - time clock of CPU time.
• CLOCK_PROCESS_CPUTIME_ID - a high-performance timer for each process from the CPU.
• CLOCK_MONOTONIC - represents a monotonous time from some unspecified starting point.
• CLOCK_REALTIME - System-wide real-time clock.

NOTE , but not all options are supported on all Linux platforms except clock_gettime (CLOCK_REALTIME), which is equivalent to gettimeofday ().

Useful link: Profiling code using clock_gettime

Answer 3

Tuomas Pelkonen has already introduced the gettimeofday method, which allows you to get time with a resolution of up to microseconds.

In his example, he goes on to double conversion. I personally wrapped the timeval structure in my own class, which stores scores in seconds and microseconds as integers and handles the add and minus operations correctly.

I prefer to store integers (with exact mathematicians), rather than getting floating point numbers and all their troubles when I can.