https://www.usenix.org/system/files/conference/nsdi18/nsdi18-geng.pdf is also a recent research paper on a similar topic which might be an interesting read if you are interested in time synchronization.
-Todd On Tue, Oct 23, 2018 at 8:47 AM Gil Tene <[email protected]> wrote: > The mean end-to-end (from writing to a socket to reading from a socket), > round-trip latency across a modern 10G+ can be brought down to 30-40usec on > modern hardware with relatively low effort or specialized equipment (e.g. > https://blog.cloudflare.com/how-to-achieve-low-latency/), and can be > driven as low as 3-5 usec with specialized hardware and software stacks > (kernel bypass, etc) (e.g. > http://www.mellanox.com/related-docs/whitepapers/HP_Mellanox_FSI%20Benchmarking%20Report%20for%2010%20%26%2040GbE.pdf > ). > > A trivial round trip ("what time do you have? [my time is X]" to "My clock > shows Y for your request sent at X" [recieved at Z]". would allow you to > measure the delta between the perceived wall clock difference between two > machines to within the round trip latency. e.g. The difference between the > clocks (at the time measured) in the above sequence is known to be (Z-Y) > +/- (Z-X). You can use various statistical techniques to more closely > estimate the bound when repeating the round trip queries many times and > across periods of time. E.g. the amazingly effective techniques used > (decades ago) by NTP to synchronize clocks to within milliseconds across > wide geographical distances and slow/jittery networks still apply even at > low latency scales (e.g. start with something like > http://www.ntp.org/ntpfaq/NTP-s-algo.htm or > https://www.cisco.com/c/en/us/about/press/internet-protocol-journal/back-issues/table-contents-58/154-ntp.html > and dig into references if interested). > > Keep in mind that at the levels you are looking at clock skew and drift > are very real things. And then there is jitter... > > On Tuesday, October 23, 2018 at 5:05:22 AM UTC-7, Himanshu Sharma wrote: >> >> As the title suggests, consider 2 servers connected via an L3 switch. How >> can we find the absolute time difference between the clocks running on the >> servers. I want to go as close as possible. >> >> Actually syncing the clocks is not possible due to some constraints so I >> want to know the time difference. Is there any opensource tool I can use >> readily. >> >> >> Many thanks in advance >> > -- > You received this message because you are subscribed to the Google Groups > "mechanical-sympathy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
