TCP loopback socket fusing

[Andre Oppermann]

On 14.09.2010 11:18, Fabien Thomas wrote:
> 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".

A sysctl to that effect is already in the patch.

-- 
Andre

> 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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>
>
>