Re: TCP loopback socket fusing

Great,

This will maybe kill the long time debate about "my loopback is slow vs linux"
To have the best of both world what about a socket option to enable/disable fusing:
can be useful when you need to see some connection "packetized".

Fabien

On 13 sept. 2010, at 13:33, Andre Oppermann wrote:

> When a TCP connection via loopback back to localhost is made the whole
> send, segmentation and receive path (with larger packets though) is still
> executed.  This has some considerable overhead.
> 
> To short-circuit the send and receive sockets on localhost TCP connections
> I've made a proof-of-concept patch that directly places the data in the
> other side's socket buffer without doing any packetization and other protocol
> overhead (like UNIX domain sockets).  The connections setup (SYN, SYN-ACK,
> ACK) and shutdown are still handled by normal TCP segments via loopback so
> that firewalling stills works.  The actual payload data during the session
> won't be seen and the sequence numbers don't move other than for SYN and FIN.
> The sequence are remain valid though.  Obviously tcpdump won't see any data
> transfers either if the connection has fused sockets.
> 
> Preliminary testing (with WITNESS and INVARIANTS enabled) has shown stable
> operation and a rough doubling of the throughput on loopback connections.
> I've tested most socket teardown cases and it behaves fine.  I'm not entirely
> sure I've got all possible path's but the way it is integrated should properly
> defuse the sockets in all situations.
> 
> Testers and feedback wanted:
> 
> http://people.freebsd.org/~andre/tcp_loopfuse-20100913.diff
> 
> -- 
> Andre
> 
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