Re: rte_event_eth_tx_adapter_enqueue() short enqueue

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Nov 27, 2024 at 11:03:31AM +0100, Mattias Rönnblom wrote:
> Hi.
> 
> Consider the following situation:
> 
> An application does
> 
> rte_event_eth_tx_adapter_enqueue()
> 
> and due to back-pressure or some other reason not all events/packets could
> be enqueued, and a count lower than the nb_events input parameter is
> returned.
> 
> The API says that "/../ the remaining events at the end of ev[] are not
> consumed and the caller has to take care of them /../".
> 
> May an event device rearrange the ev array so that any enqueue failures are
> put last in the ev array?
> 
> In other words: does the "at the end of ev[]" mean "at the end of ev[] as
> the call has completed", or is the event array supposed to be untouched, and
> thus the same events are at the end both before and after the call.
> 
> The ev array pointer is not const, so from that perspective it may be
> modified.
> 
> This situation may occur for example the bonding driver is used under the
> hood. The bonding driver does this kind of rearrangements on the ethdev
> level.
> 

Interesting question. I tend to think that we should not proclude this
reordering, as it should allow e.g  an eventdev which is short on space to
selectively enqueue only the high priority events.

Only caveat is that if we do allow the reordering we clarify the
documentation to explicitly state that it is allowed.

/Bruce