Kernel PLL graphs

Matthew Selsky Matthew.Selsky at
Wed Aug 3 21:49:41 UTC 2016

On Wed, Aug 03, 2016 at 02:24:01PM -0700, Hal Murray wrote:

> Time to make sure I've got the right number of negatives...  "I have !NO_HZ 
> set" means you have unset NO_HZ which probably means you had to build your 
> own kernel.

We build our own kernels and we boot our stratum 1 clocks with "nohz=off"

> Do you have flag3 turned on?  If so, the kernel does all the work and maxpoll 
> is essentially ignored.

We do not have flag3 turned on.  ntpd is reading the GPS via shared memory.  The GPS comes with a lightweight daemon that reads /dev/refclock0 and stuffs the time in shared memory.

> I though there was a min to maxpoll so I'm a bit surprised you could set it 
> to 1.

We had a local patch to change the minimum value of minpoll/maxpoll to 1.  Eric recently committed a similar patch upstream.

> At least for the effect I'm discussing, it only matters if you have a PPS.

We're using PCIe GPS receiver cards.


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