Re: Unix sockets via TCP on localhost: is TCP slower?

["Chris Friesen" <cfriesen@nortel.com>]

Olaf van der Spek wrote:
> On Thu, Nov 13, 2008 at 12:24 PM, Arnaldo Carvalho de Melo
> <acme@redhat.com> wrote:
>> Em Thu, Nov 13, 2008 at 12:20:44AM +0100, Olaf van der Spek escreveu:
>>> Hi,
>>>
>>> Quite often in discussions, I see people claiming Unix sockets are
>>> faster then TCP sockets on a connection that stays inside localhost.
>>> Let's say from app A to app B.
>>> Is this indeed the case and if so, how much and why?
>>> My assumption is that the kernel can optimize the 'connection' and let
>>> any performance differences disappear.
>> How much? Please measure.

Lmbench shows local tcp as noticeably slower than unix sockets on a Mac 
G5 running 2.6.27.


*Local* Communication latencies in microseconds - smaller is better
---------------------------------------------------------------
Host           OS 2p/0K  Pipe AF     UDP  RPC/   TCP  RPC/ TCP
                   ctxsw       UNIX         UDP         TCP conn
--------- ------- ----- ----- ---- ----- ----- ----- ----- ----
localhost 2.6.27  2.270  10.5 12.6  19.9  31.5  22.7  35.5  68.




*Local* Communication bandwidths in MB/s - bigger is better
-----------------------------------------------------------------------
Host          OS  Pipe AF    TCP  File   Mmap  Bcopy  Bcopy  Mem   Mem
                        UNIX      reread reread (libc) (hand) read write
--------- ------- ---- ---- ---- ------ ------ ------ ------ ---- -----
localhost 2.6.27  1368 1564 334. 1111.8 2068.8  930.3  947.0 2072 1269.




Chris