Automatic TCP send socker buffer sizing

[Andre Oppermann]

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

The patch was missing the changes to tcp_usrreq.c and socketvar.h.
I've replaced it with an updated one.  Please fetch again.

-- 
Andre