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X-BeenThere: barebox@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "barebox" X-SA-Exim-Connect-IP: 2607:7c80:54:3::133 X-SA-Exim-Mail-From: barebox-bounces+lore=pengutronix.de@lists.infradead.org X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on metis.ext.pengutronix.de X-Spam-Level: X-Spam-Status: No, score=-103.6 required=4.0 tests=AWL,BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_LOW,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE,USER_IN_WELCOMELIST,USER_IN_WHITELIST autolearn=unavailable autolearn_force=no version=3.4.2 Subject: [PATCH 8/8] tftp: add some documentation about windowsize support X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on metis.ext.pengutronix.de) Signed-off-by: Enrico Scholz --- 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 `. + +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