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

[Ferruh Yigit]

On 6/25/2020 7:49 PM, Vivien Didelot wrote:
> Hi Olivier,
> 
> On Thu, 25 Jun 2020 18:35:32 +0200, Olivier Matz <olivier.matz at 6wind.com> wrote:
>> As said by Ferruh, the unit of timestamp in mbuf is not normalized to
>> nanosecs, as seen in rte_mbuf_core.h:
>>
>> 	/** Valid if PKT_RX_TIMESTAMP is set. The unit and time reference
>> 	 * are not normalized but are always the same for a given port.
>> 	 * Some devices allow to query rte_eth_read_clock that will return the
>> 	 * current device timestamp.
>> 	 */
>> 	uint64_t timestamp;
>>
>> Using the timestamp generated from a port which is not a pmd-pcap would
>> require a conversion, using rte_eth_read_clock() on mbuf->port (assuming
>> it was not modified, which should be true except if event eth Tx adapter
>> is used).
>>
>> Also, note that the timestamp corresponds to the Rx timestamp. I think it
>> could be an issue in case the mbuf is reassembled by the application: the
>> timestamp in reassembled mbuf would be the one from the first fragment.
>>
>> So, I share Ferruh's concerns.
> 
> I think this is not totally true depending on the driver. For instance, we
> use mlx5 which already provides a timestamp conversion to nanosecs through
> libibverbs. Let me resend this patch alongside Patrick's mlx5 patches that
> implemented the needed glue, so that you may understand better the big picture
> of how we enabled hardware timestamping in PCAP capture using mlx5 and pdump.
> 

Hi Vivien,

Not sure a specific driver doing the conversion solves the issue. The check is
to 'PKT_RX_TIMESTAMP' which is generic.