Automatic TCP send socker buffer sizing
andre at freebsd.org
Thu Nov 16 22:43:48 UTC 2006
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:
The patch was missing the changes to tcp_usrreq.c and socketvar.h.
I've replaced it with an updated one. Please fetch again.
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