[ntp:questions] Which version of Linux works best?

unruh unruh at wormhole.physics.ubc.ca
Thu Mar 11 19:00:10 UTC 2010

On 2010-03-11, Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:
> In article <hn8dlq$fpu$1 at news.eternal-september.org>,
>  "David J Taylor" <david-taylor at blueyonder.co.uk.invalid> writes:
>>Yes, I know it's one of those low long is a piece of string questions, but 
>>I'm now considering a dual-core Intel Atom system, which is "Compatible 
>>with Linux" according the the very minimal blurb I have right now.  If the 
>>system is to be used purely for NTP with Linux as a serial-port GPS/PPS 
>>stratum-1 server (and, yes, I know dual-core isn't needed for that, but I 
>>might want to boot Windows-7 64-bit occasionally), and considering that I 
>>know very little about Linux, which version of Linux would the group 
>>recommend?  Does it make any difference as far as timekeeping is 
>>Two secondary questions:
>>- how much better might FreeBSD be than Linux?  Any actual measurements?
>>- and one for Bill, how much better might chrony be than official NTP? 
>>Does it have a preferred Linux, or even freeBSD?
> Modern Linux kernels don't support PPS in the sense of RFC-whateveritis.
> There is support for an ioctl that says "wake me up when a modem signal changes".
> gpsd uses that to provide PPS support.  I don't have any data.

I believe but am not sure, that that uses an interrupt. I have written (
well adapted) and parallel port interrupt service routine which writes
the time at the interrupt to a circular buffer, for reading from
/dev/gpsint, and adapted shmpps to read that and send it to the shm
refclock. tests ( sending out a signal on a parallel line connected to
the parallel interrupt line) ahows that this is good to about 1usec.
(total delay from writing to the parallel line to being read by the
interrupt routine.)
But I suspect this is not what he meant, but rather my claim that chrony
is about a factor of 3 better than ntpd in disciplining the clock. 
> If you are familiar with FreeBSD, I'd suggest that route.

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