Re: [Linuxptp-users] clockcheck - need to filter large spurious phase jumps?

[Richard C. <ric...@gm...>]

On Tue, Nov 12, 2013 at 02:28:38PM -0500, Rich Schmidt wrote:
> We use 16s update interval on our NTP servers that are synced to PTP time
> code using a Spectracom PCIe PTP card, and our system clock jitter is
> around 700 nanoseconds! Frequency changes due to temperature effects are
> not rapid in our environment.  If you run adjtime too frequently you may
> end up chasing your tail.

Regarding Spectracom, you are talking about their TimeKeeper software,
right?

>From the description on their web site it sounds like they are keeping
their own time in user space. They say their product does not require
user space or kernel modifications (but I suppose must require loading
a driver for their card). It is likely that they are intercepting
calls to the C library functions (like gettimeofday) via LD_PRELOAD.

In any case, in order to avoid comparing apples with oranges, I just
what to make it clear that phc2sys is adjusting the Linux system time
via the standard adjtimex system call.

Looking at your nov11-12.txt, it takes about 4.7 microseconds to read
the time from your PCIe card once. That is why the claim of 700 ns
jitter is surprising to me.

Thanks,
Richard