Signed-off-by: Enrico Scholz <enrico.scholz@xxxxxxxxxxxxxxxxx> --- Documentation/filesystems/tftp.rst | 38 ++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/Documentation/filesystems/tftp.rst b/Documentation/filesystems/tftp.rst index a292765e2511..8929213d3c4a 100644 --- a/Documentation/filesystems/tftp.rst +++ b/Documentation/filesystems/tftp.rst @@ -20,3 +20,41 @@ Example: In addition to the TFTP filesystem implementation, barebox does also have a :ref:`tftp command <command_tftp>`. + +RFC 7440 "windowsize" support +============================= + +barebox supports the tftp windowsize option for downloading files. It +is not implemented for uploads. + +Generally, this option greatly improves the download speed (factors +4-30 are not uncommon). But choosing a too large windowsize can have +the opposite effect. Performance depends on: + + - the network infrastructure: when the tftp server sends files with + 1Gb/s but there are components in the network (switches or the + target nic) which support only 100 Mb/s, packets will be dropped. + + The lower the internal buffers of the bottleneck components, the + lower the optimal window size. + + In practice (iMX8MP on a Netgear GS108Ev3 with a port configured to + 100 Mb/s) it had to be reduced to + + .. code-block:: console + global tftp.windowsize=26 + + for example. + + - the target network driver: datagrams from server will arive faster + than they can be processed and must be buffered internally. For + example, the `fec-imx` driver reserves place for + + .. code-block:: c + #define FEC_RBD_NUM 64 + + packets before they are dropped + + - partially the workload: copying downloaded files to ram will be + faster than burning them into flash. Latter can consume internal + buffers quicker so that windowsize might be reduced -- 2.37.2
