Accurate inter process timer on Linux

Question

I would like to measure the ping time between a sender process and a consumer.
Both processes run on the same physical host, Linux 64 bit.

I'm currently using clock_gettime(CLOCK_REALTIME, &cur_ts);. I basically capture the current timestamp cur_ts and send it to consumer process; as soon as it's being received on the other end I then invoke clock_gettime(CLOCK_REALTIME, &cur_ts); again in the second process and subtract the two times.

Is this procedure accurate to measure ping between two processes? Should I be using something different?

Thanks

Answer 1

Yes

You are using the correct interface. This is a Posix-specified HRT (High Resolution Timer) that is available in modern Loonix, and your use is the canonical standard.

For ping resolutions it probably doesn't matter, but it's possible to use CLOCK_MONOTONIC, especially for short intervals. Under other conditions, CLOCK_REALTIME may be more accurate. However, the exact meaning of these clocks is not specified by Posix, and on Linux, I believe all of them are subject to NTP adjustments. That's a good thing for long intervals, at least.

On Linux, to get access to the underlying hardware clock without NTP adjustments, you have to go off the Posix reservation and use CLOCK_MONOTONIC_RAW.

http://pubs.opengroup.org/onlinepubs/9699919799/functions/clock_gettime.html