tree 7eabe363d9c8332511d60bf22cd62e81d4e7afc3
parent 4c8620e03b1b5a0681c4fa3f706d57ee3aeada65
author Ambroz Bizjak <ambrop7@gmail.com> 1479983254 +0100
committer goldsimon <goldsimon@gmx.de> 1479983254 +0100

Optimize passing contiguous nocopy buffers to tcp_write

While TCP_OVERSIZE works only when tcp_write() is used with
TCP_WRITE_FLAG_COPY, this new code achieves
similar benefits for the use case that the caller manages their own
send buffers and passes successive chunks of those to tcp_write()
without TCP_WRITE_FLAG_COPY.

In particular, if a buffer is passed to
tcp_write() that is adjacent in memory to the previously passed
buffer, it will be combined into the previous ROM pbuf reference
whenever possible, thus extending that ROM pbuf rather than allocating
a new ROM pbuf.

For the aforementioned use case, the advantages of this code are
twofold:
1) fewer ROM pbufs need to be allocated to send the same data, and,
2) the MAC layer gets outgoing TCP packets with shorter pbuf chains.

Original patch by Ambroz Bizjak <ambrop7@gmail.com>
Edited by David van Moolenbroek <david@minix3.org>
Signed-off-by: goldsimon <goldsimon@gmx.de>