<p>I have an application that depends on gpsd and ntpd to accurately set the system time on a linux machine.</p>

<p>gpsd is fed NMEA + PPS</p>

<p>The application is punping ~25MB per second over the network and I think the loading on the system is causing jitter in the time somehow. (loaded PCI express bus causing irregular interrupt latency)</p>

<p>I have another machine that is not loaded at all that I could setup to read the GPS and act as an NTP server for the loaded machine. (the loaded machine would be getting startum 1 ???)</p>

<p><strong>How accurate can I expect the time to be from a stratum 0 NTP server on the same subnet on Ethernet?</strong></p>

<p>I hope this is not too off topic, I am sure sometime someone else will be happy the answer is documented here. ;-)</p>

Best info I could find on
NTP accuracy
, seems to point at 1-2 ms in a LAN setting:
NTP v4 with kernel mods to support it, is capable of much better than 1ms accuracy, possibly as good as 1ns.  According to [Dave Mills] article, NTP v3 is accurate to 1-2ms in a LAN and 10s of ms in WAN nets.
http://www.cis.udel.edu/~mills/ntp.html
Other articles suggest that with an accurate time source, such as a GPS time source, NTP is accurate to 50us, but the links on the Linux kernel support say that accuracy of a few ms are possible.
http://www.atomic-clock.galleon.eu.com/support/ntp-time-server-accuracy.html
Another article says that it is dependent on the predictability of network delays (i.e. a low jitter network).
http://www.postel.org/pipermail/end2end-interest/2003-April/002925.html