linux - print current time with microsecond precision on multi-processor system

Question

How can I print current system time with microsecond (or, better, nanosecond) precision? I need this time to be consistent between all system processors. If this is not possible than I want it to be consistent between all processor cores.

I've tried clock_gettime(CLOCK_REALTIME but I suspect it produce different result at least when running on different processors.

Check [here](http://stackoverflow.com/questions/5833094/get-a-timestamp-in-c-in-microseconds). — Arnab Nandy, Dec 23 '14 at 07:58
Take a look at [`std::chrono::high_resolution_clock`](http://en.cppreference.com/w/cpp/chrono/high_resolution_clock) — πάντα ῥεῖ, Dec 23 '14 at 07:58
if high_resolution_clock works accross different phissical procesors? — Oleg Vazhnev, Dec 23 '14 at 19:52
what is better feets low-latency requirements - high_resulution_clock or clock_gettime or gettimeofday ? — Oleg Vazhnev, Dec 23 '14 at 20:01

score 2 · Answer 1 · answered Dec 23 '14 at 08:18

Sounds to me what you really want is CLOCK_MONOTONIC_RAW (or just CLOCK_MONOTONIC) . The raw clock measures time starting at a fixed point and queries a pure hardware-based clock. On Linux this fixed time point is the time of startup. Changes in the system time do not effect this clock (Summer/wintertime, etc.)

You can check the resolution of the clock in your system with a call to clock_getres(clockid_t clk_id, struct timespec *res);

Both gettime and getres take a timespec structure which holds two integers: seconds and nanoseconds. So the software is there, you just need a (hardware) clock capable of supplying the nanosecond resolution.

Man pages of the two functions:

http://man7.org/linux/man-pages/man2/clock_gettime.2.html & http://linux.die.net/man/3/clock_gettime

If you have access to the book "Linux Programming Interface" by Michael Kerrisk check out chapter 23 paragraph 5 (POSIX Clocks). When it comes to basic Linux programming this book has given me more answers than even StackOverflow has!

Even more important is reading [time(7)](http://man7.org/linux/man-pages/man7/time.7.html) — Basile Starynkevitch, Dec 23 '14 at 09:23
is it guaranteed that CLOCK_MONOTONIC_RAW can be used across physical processors? — Oleg Vazhnev, Dec 23 '14 at 19:42
The monotonic clock is for the system. So, the way I read it is that no matter how many cores you have the time will be the same across all of them. It is answered in this SO question too: [Is clock monotonic process or thread specific.](https://stackoverflow.com/questions/4943733/is-clock-monotonic-process-or-thread-specific). — Nathilion, Dec 25 '14 at 17:09

linux - print current time with microsecond precision on multi-processor system

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