[dpdk-dev] [RFC PATCH 3/3] net/pcap: support hardware Tx timestamps

[PATRICK KEROULAS]

On Fri, Jun 26, 2020 at 2:48 AM Olivier Matz <olivier.matz at 6wind.com> wrote:
> I don't get why you expect that timestamp to be in nanoseconds.
> The conversion is done in librte_pdump (in the previous patch),
> but it won't work if the library is not used, right?
>

You're right Olivier. I took advantage of the definition of mbuf->timestamp
as being "not normalized". The proposed conversion needs NIC clock info
which can't be accessed from the secondary process. Do you have a better
suggestion? Should I set a user flag in mbuf for nanoseconds?

> Out of curiosity, can you explain your motivation for using the hardware
> timestamp? Is it faster? More accurate? (knowing it timestamps the Rx
> operation, not the Tx)

Accuracy is our requirement in the broadcast industry (and probably
in finance as well) where core systems are very time sensitive. Our
application uses the NIC mostly as a receiver for UDP stream monitoring
in order to measure the network propagation delay and jitter. Using SW Rx
timestamps completely breaks this requirement.