Re: Leveraging PTM

On Thu, Sep 07, 2023 at 10:49:50AM +0700, James Clark wrote:
> I'm curious about how well this works when there are multiple switches
> between server/client. I've got two slightly different variants of this
> switch, so I could potentially test this.

Not exactly the same thing, but I simulated 4 switches by splitting
the single switch into 4 VLANs and daisy chaining the 4 pairs of
ports.

The jitter observed by chrony doubled when not using the PTP
correction, but there was no change at all when using the correction.
It still seems symmetric and jitter of only about 10 ns, which I think
mostly comes from the I210 resolution (125MHz clock).

Here are some plots:
https://i.imgur.com/O9FngmX.png

I'd be curious to see some tests with PTM.

I also tested the switch with PTP in the other supported modes. There
are some issues:
- 2-step E2E and both 1-step and 2-step P2P transparent clocks
  insert a VLAN tag to the sync/follow up messages if using UDP
  transport, which completely breaks synchronization. L2 transport
  works ok.
- Boundary clock doesn't lock. It's constantly switching between
  FREQ_LOCKING and PHASE_LOCKING states. I tried changing the PID
  constants to few different values, but that didn't seem to help.
- Boundary clock doesn't adopt grandmaster identity from its master.
  Maybe that happens only when it locks.

-- 
Miroslav Lichvar


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