[lwip-devel] [task #6827] etharp could need some tuning

[Simon Goldschmidt]

Follow-up Comment #20, task #6827 (project lwip):

I've just come up with an even better idea to tune the speed of
etharp_output: We could store the last used arp_table index in every ip_pcb.
Thus, if every ip_pcb knows its last used index, every TCP-connection should
have to look only once which index it has to use, and for RAW and UDP pcbs,
it should also significantly reduce the number of array-searches.

This would move the one-entry-cache from etharp into a one-entry-cache for
every single connection. And since it is an integer only, it's performance
gain at very low RAM usage.

The only question is how to neatly integrate it into the netif->output ->
etharp_output calling chain. Maybe we can pass on the ip_pcb in addition to
the ipaddr? Since it has to do with IP anyway, it wouldn't be that far away
from what we are doing now (passing the ipaddr, I mean). And we could still
allow a NULL-pointer so that nothing is done. If != NULL, etharp_output could
update the index every time.

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