Automatic TCP send socker buffer sizing

[Mark Atkinson]

Andre Oppermann wrote:

> This is a patch adding automatic TCP send socket buffer sizing.  Normally
> the socket buffers are static (either derived from global defaults or set
> with setsockopt) and do not adapt to real network conditions.  Two things
> happen: a) your socket buffers are too small and you can't reach the full
> potential of the network between both hosts; b) your socket buffers are
> too big and you waste a lot of kernel memory for data just sitting around.
> 
> With automatic TCP send socket buffers we can start with a small buffer
> and quickly grow it in parallel with the TCP congestion window to match
> real network conditions.
> 
> FreeBSD has a default 32K send socket buffer.  This supports a maximal
> transfer rate of only slightly more than 2Mbit/s on a 100ms RTT trans-
> continental link.  Or at 200ms just above 1Mbit/s.  With TCP send buffer
> auto scaling and the default values below it supports 20Mbit/s at 100ms
> and 10Mbit/s at 200ms.  That's an improvement of factor 10, or 1000%.
> 
> New sysctl's are:
> 
>   net.inet.tcp.sndbuf_auto=1  (enabled)
>   net.inet.tcp.sndbuf_inc=8192        (8K, step size)
>   net.inet.tcp.sndbuf_max=262144      (256K, growth limit)
> 
> The patch is available here:
> 
>   http://people.freebsd.org/~andre/tcp_auto_sndbuf-20061116.diff
> 
> Any testers, especially with busy FTP servers, are very welcome.

Did some minimal testing and it appears to apply cleanly and log:

ov 17 11:15:27 ftp kernel: tcp_output: inc sockbuf, old 33304, new 41496,
sb_cc 31776, snd_wnd 40544, sendwnd 20272
Nov 17 11:15:27 ftp kernel: tcp_output: inc sockbuf, old 41496, new 49688,
sb_cc 38232, snd_wnd 46336, sendwnd 27512
Nov 17 11:15:27 ftp kernel: tcp_output: inc sockbuf, old 49688, new 57880,
sb_cc 46960, snd_wnd 63712, sendwnd 40544
Nov 17 11:15:27 ftp kernel: tcp_output: inc sockbuf, old 57880, new 66072,
sb_cc 55568, snd_wnd 63712, sendwnd 60816
Nov 17 11:15:27 ftp kernel: tcp_output: inc sockbuf, old 66072, new 74264,
sb_cc 65168, snd_wnd 63712, sendwnd 63712
Nov 17 11:15:27 ftp kernel: tcp_output: inc sockbuf, old 74264, new 82456,
sb_cc 65168, snd_wnd 63712, sendwnd 63712

-- 
Mark Atkinson
atkin901 at yahoo.com
(!wired)?(coffee++):(wired);