Kernel PLL, from IRC
hmurray at megapathdsl.net
Wed Sep 28 18:14:49 UTC 2016
I have a hard time believing a PLL
running at user timer interrupt time
can be anywhere as good as a kerenl
PLL running at TICK intervals.
There are two parts to this discussion. There is the PPS time stamp and the
The PPS time stamp gives you the data to work with. The work can be done in
user space or in the kernel. New samples arrive every second. Suppose I use
the same algorithm. Running the code in user space adds a few sub-ms kernel
calls. (I'm assuming the scheduler cooperates.) I don't think that minor
delay will be significant.
The kernel PLL is probably using different parameters than ntpd.
Is there a simple switch to select
between the two? I could run some
It's a flag on the PPS driver. But you will probably have to build a kernel.
Most distros ship with the magic feature disabled.
yes, best to measure
Check your clockstats on your minpoll-0 runs and see if it really was running
at 0. On my quick tries, it was actually running at 1 (2 samples per batch)
I didn't track it down.
These are my opinions. I hate spam.
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