On Feb 07, 2017, at 06:01, Miroslav Lichvar [off-list ref] wrote:

1) new rx_filter for NTP

  Some NICs can't timestamp all received packets and are currently
  unusable for NTP with HW timestamping. The new filter would allow
  NTP support in new NICs and adding support to existing NICs with
  firmware/driver updates. The filter would apply to IPv4 and IPv6
  UDP packets received from or sent to the port number 123.

I think this is a good idea. Even if the hardware doesn’t support it, the filtering could be done in the kernel. Save a huge number of context switches.

4) allow sockets to use both SW and HW TX timestamping at the same time

  When using a socket which is not bound to a specific interface, it
  would be nice to get transmit SW timestamps when HW timestamps are
  missing. I suspect it's difficult to predict if a HW timestamp will
  be available. Maybe it would be acceptable to get from the error
  queue two messages per transmission if the interface supports both
  SW and HW timestamping?

Highly agreed. The current interface pretty much forces a socket per physical interface, which should not be necessary.

5) new SO_TIMESTAMPING options to get transposed RX timestamps

  PTP uses preamble RX timestamps, but NTP works with trailer RX
  timestamps. This means NTP implementations currently need to
  transpose HW RX timestamps. The calculation requires the link speed
  and the length of the packet at layer 2. It seems this can be
  reliably done only using raw sockets. It would be very nice if the
  kernel could tranpose the timestamps automatically.

  The existing SOF_TIMESTAMPING_RX_HARDWARE flag could be aliased to
  SOF_TIMESTAMPING_RX_HARDWARE_PREAMBLE and the new flag could be
  SOF_TIMESTAMPING_RX_HARDWARE_TRAILER.

  PTP has a similar problem with SW RX timestamps, which are closer
  to the trailer timestamps rather than preamble timestamps. A new
  SOF_TIMESTAMPING_RX_SOFTWARE_PREAMBLE flag could be added for PTP
  implementations to get transposed timestamps in order to improve
  accuracy.

Also highly agreed.

Denny