On 02/17/2017 04:51 PM, Jan Blunck wrote:

On Fri, Feb 17, 2017 at 1:49 PM, Nélio Laranjeiro
[off-list ref] wrote:

quoted

Hi Olivier, Jan,

On Fri, Feb 17, 2017 at 11:51:53AM +0100, Olivier Matz wrote:

quoted

Hi Jan,

On Thu, 16 Feb 2017 18:26:39 +0100, Jan Blunck [off-list ref]
wrote:

quoted

If we talk about setting the timestamp value in the RX path this
implicitly means software timestamps. Hardware timestamping usually
works by letting the hardware inject sync events for coarse time
tracking and additionally injecting fine granular per-packet ticks at
a specific offset in the packet. Out of performance reasons I don't
think it makes sense to extract this during the burst and write it
into the mbuf again.

 From what I've understand, at least it does not work like this for
mellanox NICs: timestamp is a metadata attached to a rx packet. But
maybe they (and other NIC vendors interrested in the feature) can
confirm or not.

Olivier is right, this timestamp information is returned by the hardware
as the other fields describing the Rx packet (length, RSS hash, checksum
...).  The PMD only copy it into the Mbuf.

Indeed, for Mellanox the timestamp is stored in the CQ entry.
Solarflares write it relative to the packet header.

Confirmed. We have pseudo-header just before the packet itself and 
timestamp is put to pseudo-header by the HW.