High UNIX socket latency

High UNIX socket latency

[Jakob Østergaard]

Hello all,

One program that creates a pipe between two processes and measures
the ping/pong latency of messages between the two processes gives
me something like;

1000 iterations - ping/pong time
max =   3495 us
min =      6 us
avg = 47.212 us

In another application where I use a UNIX STREAM socket, I get
a typical latency of one send() of around 1 ms.

I cannot set TCP_NODELAY on a UNIX socket, and I can't really
see why I get the high latency.   Is there some undocumented
option like TCP_NODELAY for UNIX STREAM connections, or are there
other tricks I can play to get the latency down ?

One process does a send(), the other one does a select() and a
recv() - and the time from the send() to the recv() is around 1 ms
which I think seems far too high.

Hints, suggestions ?

 Thank you

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:

Re: High UNIX socket latency

[GOTO Masanori]

At Tue, 13 Nov 2001 12:51:26 +0100,
Jakob Ostergaard <jakob@unthought.net> wrote:
> In another application where I use a UNIX STREAM socket, I get
> a typical latency of one send() of around 1 ms.
> 
> I cannot set TCP_NODELAY on a UNIX socket, and I can't really
> see why I get the high latency.   Is there some undocumented
> option like TCP_NODELAY for UNIX STREAM connections, or are there
> other tricks I can play to get the latency down ?
>
> One process does a send(), the other one does a select() and a
> recv() - and the time from the send() to the recv() is around 1 ms
> which I think seems far too high.

I think more details are needed... kernel version, packet size, 
select timeout, your program/environment, the result of
average responce time and each responce time, throughput, etc.

-- gotom