Re: [dpdk-dev] mlx5 & pdump: convert HW timestamps to nanoseconds

[PATRICK KEROULAS <patrick.keroulas@radio-canada.ca>]

> > I'm trying to build an accurate capture device based on Mellanox
> > Connect-X5 with following requirements:
> > - capture every incoming packets with hardware timestamps
> > - output: pcap with timestamps in nanoseconds
> > My problem is that the packets forwarded to `dpdk-pdump` carry raw
> > timestamps from NIC clock.
>
> Please could you describe how you use dpdk-pdump?
> Is it using the mlx5 PMD or pcap PMD?

We're actually using both:
# Rx, receive from NIC
CONFIG_RTE_LIBRTE_MLX5_PMD=y
# Tx, output to pcap file
CONFIG_RTE_LIBRTE_PMD_PCAP=y

$ sudo ./build/app/testpmd -w 0000:01:00.0 -w 0000:01:00.1 -n4 --
--enable-rx-timestamp
$ dpdk-pdump -- --pdump 'port=0,queue=*,rx-dev=capture.pcap'

We've sent this placeholder with the intention to start the discussion.
https://github.com/DPDK/dpdk/commit/bd371e1ba5bfc5b7092d712a01bbc28799fd58bc.patch
https://github.com/DPDK/dpdk/commit/e6f5c731c4ab27ab80b229af98c9b3d257e13843.patch

> > mlx5 part of libibverbs includes a ts-to-ns converter which takes the
> > instantaneous clock info. It's unused in dpdk so far. I've tested it in the
> > device/port init routine and the result looks reliable. Since this approach
> > looks very simple, compared to the time sync mechanism, I'm trying to
> > integrate.
> >
> > The conversion should occur in the primary process (testpmd) I suppose.
> > 1) The needed clock info derives from ethernet device. Is it possible to
> >    access that struct from a rx callback?
> > 2) how to attach the nanosecond to mbuf so that `pdump` catches it?
> >    (workaround: copy `mbuf->udata64` in forwarded packets.)
> > 3) any other idea?
>
> The timestamp is carried in mbuf.
> Then the conversion must be done by the ethdev caller (application or
> any other upper layer).

What if the converter function needs a clock_info?
https://github.com/linux-rdma/rdma-core/blob/7af01c79e00555207dee6132d72e7bfc1bb5485e/providers/mlx5/mlx5dv.h#L1201
I'm affraid this info may change by the time the converter is called
by upper layer.

Thanks,
PK