From: Mingbao Sun <redacted>

Hey Mingbao,

congestion-control could have a noticeable impaction on the
performance of TCP-based communications. This is of course true
to NVMe_over_TCP.

Different congestion-controls (e.g., cubic, dctcp) are suitable for
different scenarios. Proper adoption of congestion control would benefit
the performance. On the contrary, the performance could be destroyed.

Though we can specify the congestion-control of NVMe_over_TCP via
writing '/proc/sys/net/ipv4/tcp_congestion_control', but this also
changes the congestion-control of all the future TCP sockets that
have not been explicitly assigned the congestion-control, thus bringing
potential impaction on their performance.

So it makes sense to make NVMe_over_TCP support specifying the
congestion-control. And this commit addresses the target side.

Implementation approach:
the following new file entry was created for user to specify the
congestion-control of each nvmet port.
'/sys/kernel/config/nvmet/ports/X/tcp_congestion'
Then later in nvmet_tcp_add_port, the specified congestion-control
would be applied to the listening socket of the nvmet port.

Please see my comments on the host side patch.

In addition, specifically on the chosen interface, why should this
be port specific? What is the use-case to configure this per-port?