Yo Hal! On Wed, 28 Sep 2016 11:14:49 -0700 Hal Murray <[email protected]> wrote:
> gemiller
> 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 PLL.
No. PPS is unrelated to the kernel PPL. It is a totally separate
kernel module.
> The PPS time stamp gives you the data to work with.
Yes.
> The work can be
> done in user space or in the kernel.
Yes, but not as well in user space.
> New samples arrive every
> second.
No. Twice a second. But now you are confusing the PPS with the PLL.
> Suppose I use the same algorithm. Running the code in user
> space adds a few sub-ms kernel calls.
And a LOT more jitter.
> (I'm assuming the scheduler
> cooperates.)
Bad assumption.
> I don't think that minor delay will be significant.
Agreed, but the jitter is. Also the frequency of updates is
different by orders of magnitude.
> The kernel PLL is probably using different parameters than ntpd.
As I have just seen. Very dufferent results.
> gemiller
> yes, best to measure
>
> Check your clockstats on your minpoll-0 runs and see if it really was
> running at 0.
Yes, it was. That is the recent bug fixes.
> On my quick tries, it was actually running at 1 (2
> samples per batch) I didn't track it down.
Until Sep 26, then it got fixed. But once again, unrelated to PPS or
PLL.
RGDS
GARY
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