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SubjectRe: anyone ever done multicast AF_UNIX sockets?
David S. Miller wrote:
> From: Chris Friesen <>
> Date: Mon, 03 Mar 2003 13:07:45 -0500
> Suppose I have a process that waits on UDP packets, the unified local
> IPC that we're discussing, other unix sockets, and stdin. It's awfully
> nice if the local IPC can be handled using the same select/poll
> mechanism as all the other messaging.
> So use UDP, you still haven't backed up your performance
> claims. Experiment, set the SO_NO_CHECK socket option to
> "1" and see if that makes a difference performance wise
> for local clients.

I did provide numbers for UDP latency, which is more critical for my own
application since most messages fit within a single packet. I haven't
done UDP bandwidth testing--I need to check how lmbench did it for the
unix socket and do the same for UDP. Local TCP was far slower than unix
sockets though.

> But if performance is "so important", then you shouldn't really be
> shying away from the shared memory suggestion and nothing is going to
> top that (it eliminates all the copies, using flat out AF_UNIX over
> UDP only truly eliminates some header processing, nothing more, the
> copies are still there with AF_UNIX).

Yes, I realize that the receiver still has to do a copy. With large
messages this could be an issue. With small messages, I had assumed
that the cost of a recv() wouldn't be that much worse than the cost of
the sender doing a kill() to alert the receiver that a message is
waiting. Maybe I was wrong.

It might be interesting to try a combination of sysV msg queue and
signals to see how it stacks up. Project for tonight.


Chris Friesen | MailStop: 043/33/F10
Nortel Networks | work: (613) 765-0557
3500 Carling Avenue | fax: (613) 765-2986
Nepean, ON K2H 8E9 Canada | email:

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