Re: [dpdk-dev] [RFC PATCH 1/3] net/mlx5: add timestamp-to-ns converter from libibverbs

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

On Fri, Jun 26, 2020 at 2:41 AM Olivier Matz <olivier.matz@6wind.com> wrote:
> Should mlx5dv_get_clock_info() be called for each convesion? In the man
> page [1], we can read this:
>
>        If the clock_info becomes too old then time conversion will return
>        wrong conversion results.  The user must ensure that
>        mlx5dv_get_clock_info(3) is called at least once every
>        max_clock_info_update_nsec as returned by the mlx5dv_query_device(3)
>        function.
>
> I understand this as mlx5dv_get_clock_info() being slower than
> mlx5dv_ts_to_ns(), and should not be called for each packet.

Right. I plan to use rte_timer (like in drivers/net/ena/) to query clock info
periodically.

>
> I suppose that when rdma-core library does a conversion to nanosec, it
> takes in account the fact that system and device are not synchronized
> (are they?).

PTP daemon like linuxptp is in charge of syncing both device and system
clocks with external master.

Thanks.
PK