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From: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
To: barebox@lists.infradead.org
Cc: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Subject: [PATCH 8/8] tftp: add some documentation about windowsize support
Date: Sun, 28 Aug 2022 16:02:31 +0200	[thread overview]
Message-ID: <20220828140231.930643-9-enrico.scholz@sigma-chemnitz.de> (raw)
In-Reply-To: <20220828140231.930643-1-enrico.scholz@sigma-chemnitz.de>

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
---
 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




  parent reply	other threads:[~2022-08-28 14:05 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-28 14:02 [PATCH 0/8] tftp fixups Enrico Scholz
2022-08-28 14:02 ` [PATCH 1/8] tftp: make debug_assert() critical when selftest is enabled Enrico Scholz
2022-08-28 14:02 ` [PATCH 2/8] tftp: remove sanity check of first block Enrico Scholz
2022-08-28 14:02 ` [PATCH 3/8] tftp: split out allocation and cache initialization Enrico Scholz
2022-08-28 14:02 ` [PATCH 4/8] tftp: accept OACK + DATA datagrams only in certain states Enrico Scholz
2022-08-28 14:02 ` [PATCH 5/8] tftp: support non rfc 2347 servers Enrico Scholz
2022-08-28 14:02 ` [PATCH 6/8] tftp: do not set 'tsize' in wrq requests Enrico Scholz
2022-08-28 14:02 ` [PATCH 7/8] tftp: fix WRQ support Enrico Scholz
2022-08-28 14:02 ` Enrico Scholz [this message]
2022-08-29 10:52 ` [PATCH 0/8] tftp fixups Ahmad Fatoum
2022-08-30  7:30   ` Sascha Hauer

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