Callback or hook into completion queues?

[Stephen Hemminger]

On Tue, 7 Mar 2023 17:07:41 -0500
fwefew 4t4tg <7532yahoo at gmail.com> wrote:

> Once I call rte_eth_tx_burst() (Mellanox Connect5-LX) is there a way to
> inspect or get a callback when transmitted packets go into the NIC's
> completion queue?

Not in DPDK.

> 
> This is related to the earlier question on timestamping with rdtsc().
> Ideally I'd take the timestamp as soon (close) to the time the packet is on
> the wire.


> 
> I've looked at tx callbacks however this is invoked as the packet is about
> to go into the "hardware queue for transmission" meaning there's lot's of
> work + serialization of packet's data to electrical signals at NIC
> bandwidth to come before the packet is on the wire.
> 
> The ideal time to get run rdtsc() is when the NIC delivers a completion
> event to a CQ for packets sent.
> 
> Presumably there's something in the mlx5 driver or perhaps DMA library to
> do this?

Not that I have ever seen.