[time-nuts] Re: NIST NTP servers way off for anyone else?

[Hal Murray]

alec at unifiedmathematics.com said:
> I've seen SO_TIMESTAMP and friends in ethtool but I have no idea what it  is
> or how it works, can you point me in the right direction please? 

man 7 socket on a Linux box.  Then man recvmsg and man cmsg

There are several variations on various OSes.


The basic idea is that the OS input processing grabs a time stamp when the 
packet arrives.  On Linux, that's done by the kernel thread that looks in the 
packet headers to figure out which input queue the packet goes on.

The basic idea is that you get a time stamp when the packet arrives rather 
than when the user program gets around to read/recv-ing it.

-- 
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