Subject: Re: TCP socket buffers auto sizing
To: Rui Paulo <>
From: Zafer Aydogan <>
List: tech-net
Date: 02/04/2007 18:27:15
Definitely. It would be great.


2007/2/4, Rui Paulo <>:
> FreeBSD has done this:
> <quote>
> Auto sizing TCP socket buffers.
> 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 and receive 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%. For the receive side it looks slightly better with a default of
> 64K buffer size.
> New sysctls are:
>   net.inet.tcp.sendbuf_auto=1 (enabled)
>   net.inet.tcp.sendbuf_inc=8192 (8K, step size)
>   net.inet.tcp.sendbuf_max=262144 (256K, growth limit)
>   net.inet.tcp.recvbuf_auto=1 (enabled)
>   net.inet.tcp.recvbuf_inc=16384 (16K, step size)
>   net.inet.tcp.recvbuf_max=262144 (256K, growth limit)
> </quote>
> Maybe we should too ?
> --
> Rui Paulo -