[FS#105] lantiq: high latency on adsl lines using pppo[ae]

[LEDE Bugs]

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FS#105 - lantiq: high latency on adsl lines using pppo[ae]
User who did this: Alexander Couzens (lynxis)
Task details edited:
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based on the thread 
[LEDE-DEV] [OpenWrt-Devel] latency on PPPoA ADSL Annex A on	using Lantiq

http://lists.infradead.org/pipermail/lede-dev/2016-August/002138.html

When using ssh onto the box via adsl, there is a high latency.
The last 3.18 version of lede works. Known good:

  * 161179f40bd7899516518f3844fea28c6dd86efc r47130

Known broken versions:

  * 2795592d913ba8ba57ba537d40714407ea463426 r47131
  * 2a0e1b7f8d59f795abb29d20007822f0da232c43 r47958

mkresin also has a patch for lantiq+4.0, which also has a high latency.
blogic mentioned linux commit 7424ce65065852bdf7a040bf2490da4a8fc4b464 [atm] switch vcc_sendmsg() to copy_from_iter() could be the issue.

Also an interesting side-effect. setup a uhttpd on the device and serve a file to the internet is very slow (using 4mb file random data). it only uploads 5kb/s
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=105