[OpenWrt-Devel] Lantiq xrx200: PTM issues

[Martin Schiller]

Update:

I've found out now that the ENOBUFS is set by __ip_append_data,
because sk_wmem_alloc "overflows".

Martin


On 2020-01-20 07:09, Martin Schiller wrote:
> Hi!
> 
> I have discovered the following problem:
> 
> If you have established a PPPoE session via VDSL / PTM connection incl.
> VLAN tagging and send data with a relatively small send buffer
> (SO_SNDBUF), then an ENOBUFS always comes back.
> 
> We first noticed this with stagnating data transfers over an OpenVPN
> connection.
> 
> Also with iputils-ping, since by default the send buffer is relatively
> small.
> 
> You can also force this with busybox ping by using
> 
> echo "5000"> / proc / sys / net / core / wmem_default
> 
> minimizes the system default value.
> 
> Then you send pings with a packet size of e.g. 4000 bytes and the
> second package is already in the pants:
> 
> ------------------------------------------------------------
> root @ OpenWrt: ~ # ping -s4000 10.200.1.142
> PING 10.200.1.142 (10.200.1.142): 4000 data bytes
> 4008 bytes from 10.200.1.142: seq = 0 ttl = 63 time = 20.519 ms
> ping: sendto: No buffer space available
> root @ OpenWrt: ~ #
> ------------------------------------------------------------
> 
> So it should be easily reproducible for everyone.
> 
> Traffic that is only routed through the router is not affected.
> 
> The manpage of sendto says:
> -----------------------------------------------------------------------
> ENOBUFS
>     The output queue for a network interface was full. This generally
>     indicates that the interface has stopped sending, but may be caused
>     by transient congestion. (Normally, this does not occur in Linux.
>     Packets are just silently dropped when a device queue overflows.)
> -----------------------------------------------------------------------
> 
> But all former packets have already been transmitted.
> 
> This issue seems to be in there since lede-17.01.
> 
> I can't reproduce it with owrt-15.05.
> 
> Does anyone have any idea how to solve the problem?
> 
> Martin
> 
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> openwrt-devel at lists.openwrt.org
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