Re: Low capped TCP network speeds over the Internet

[mlelstv%serpens.de@localhost (Michael van Elst)]

z411%omaera.org@localhost (z411) writes:

>UDP speeds are great, but NetBSD specifically has an issue with
>TCP/HTTP. The speed seems to be capped to exactly 986 KB/s and it's very
>unstable (congestion handling issues I assume).

>I tried tuning the following:

>net.inet.tcp.recvbuf_auto=1
>net.inet.tcp.sendbuf_auto=1
>net.bpf.jit=1
>net.bpf.maxbufsize=4194304
>net.inet.tcp.sendbuf_max=16777216
>net.inet.tcp.recvbuf_max=16777216
>net.inet.ip.ifq.maxlen=4096
>net.inet.tcp.mssdflt=1072


You need to increase kern.sbmax too, this is a global limit on
the socket buffer size. The default is 256kB, so at 200ms RTT
you are limited to about 256kB/200ms ~ 10Mbit/s.

If you have many connections you may also need to increase
kern.somaxkva that limits how much memory can be allocated
to the network in total.


>Since post-tuning it's very stable I don't think it's about congestion
>anymore - but I'm not sure why I'm hitting this hard cap, even after
>increasing the buffer sizes. Could it be that NetBSD is not increasing
>the window size?

NetBSD will grow the window and has window scaling enabled by default.
However, it is very slow growing the send window after a congestion event.