Date: Thu, 01 Mar 2007 15:27:52 +0100 From: Andre Oppermann <andre@freebsd.org> To: freebsd-current@freebsd.org, freebsd-net@freebsd.org Cc: gallatin@freebsd.org, rwatson@freebsd.org, kmacy@freebsd.org Subject: Large TCP send socket buffer optimizations Message-ID: <45E6E2E8.5060408@freebsd.org>
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With the TCP socket buffer autosizing and generally larger socket buffers for high bandwidth and high delay connections tcp_output() has become increasingly inefficient for sending segments. For every segment sent it is traversing the entire socket buffer mbuf chain until it finds the offset to continue from. Usually this is close to the end of the chain. Once it got past a few dozen mbufs it starts to bust the CPU caches and performance starts to fall off. This patch solves the problem by maintaining an offset pointer in the socket buffer to give tcp_output() the closest mbuf right away avoiding the traversal from the beginning. With this patch we should be able to compete nicely for the Internet land speed record again. The patch is here: http://people.freebsd.org/~andre/sockbuf_sndptr-20070301.diff Any testing, especially on 10Gig cards, and feedback appreciated. -- Andre
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