Re: [PATCH v01] net/af_packet: add rollover and defrag options

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 29 Oct 2024 15:48:05 +0200
Gur Stavi <gur.stavi@huawei.com> wrote:

> net_af_packet PMD multi "queue" support relies on Linux FANOUT capability.
> Linux FANOUT is a SW based load balancer that is similar to HW RSS which is
> more common for DPDK PMDs. Instead of multiple HW descriptor queues, AF PACKET
> uses multiple sockets.
> HW RSS will typically drop a packet if its selected RX queue is empty. However,
> Linux FANOUT, as a SW load balancer, can be configured to avoid this packet
> drop by rolling over to the next socket.
> This rollover functionality was ALWAYS enabled in net_af_packet. It is
> surrounded by ifdef, but only to allow compilation on ancient Linux versions
> that did not have it.
> 
> Since DPDK applications are usually designed for HW based PMDs, this rollover
> functionality, which the developers are likely unaware of, could be confusing.
> 
> Another option that is part of Linux FANOUT is DEFRAG that instructs Linux to
> compose complete IP packet out of fragments before delivering it to the PACKET
> socket. Again, this behavior typically does not exist for HW based PMDs and may
> confuse users.
> 
> This patch adds 2 options to control these features:
> rollover=[0|1],defrag=[0|1]
> For backward compatibility both features are enabled by default even though most
> users will probably want both of them disabled.
> 
> Signed-off-by: Gur Stavi <gur.stavi@huawei.com>
> ---

Makes sense to expose kernel options. But have all combinations been tested?