CODEWITHSUNDEEP
c++linux
Oleg Vazhnev
Oleg Vazhnev

Reputation: 24067

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

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.

Upvotes: 0

Views: 750

Answers (1)

Nathilion
Nathilion

Reputation: 329

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!

Upvotes: 2

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