Date: Thu, 16 Nov 2006 19:50:57 +0100 From: Andre Oppermann <andre@freebsd.org> To: freebsd-current@freebsd.org Cc: freebsd-net@freebsd.org Subject: Automatic TCP send socker buffer sizing Message-ID: <455CB311.8040301@freebsd.org>
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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. -- Andre
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