jamal wrote:
On Thu, 27 Feb 2003, Chris Friesen wrote:
It is fairly common to want to distribute information between a single
sender and multiple receivers on a single box.
Multicast IP sockets are one possibility, but then you have additional
overhead in the IP stack.
I think this is a _very weak_ reason.
Without addressing any of your other arguements, can you describe what
such painful overhead you are talking about? Did you do any measurements
and under what circumstances are unix sockets vs say localhost bound
udp sockets are different? I am not looking for hand waving reason of
"but theres an IP stack".
From lmbench local communication tests:
This is a multiproc 1GHz G4
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
pcary0z0. Linux 2.4.18- 0.600 3.756 6.58 10.2 26.4 13.8 36.9 599K
pcary0z0. Linux 2.4.18- 0.590 3.766 6.43 10.1 26.7 13.9 37.2 59.1
This is a 400MHz uniproc G4
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
zcarm0pd. Linux 2.2.17- 1.710 9.888 21.3 26.4 59.4 43.0 105.4 146.
zcarm0pd. Linux 2.2.17- 1.740 9.866 22.2 26.3 60.4 43.1 106.7 147.
This is a 1.8GHz P4
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
pcard0ks. Linux 2.4.18- 1.740 10.4 15.9 20.1 33.1 23.5 44.3 72.7
pcard0ks. Linux 2.4.18- 10.3 16.1 19.8 36.3 22.8 43.6 74.1
pcard0ks. Linux 2.4.18- 1.560 10.6 16.0 23.4 38.1 36.1 44.6 77.4
From these numbers, UDP has 18%-44% higher latency than AF_UNIX, with
the difference going up as the machine speed goes up.
Aside from that, IP multicast doesn't seem to work properly. I enabled
multicast on lo and disabled it on eth0, and a ping to 224.0.0.1 still
got responses from all the multicast-capable hosts on the network. From
userspace, multicast unix would be *simple* to use, as in totally
transparent.
The other reason why I would like to see this happen is that it just
makes *sense*, at least to me. We've got multicast IP, so multicast
unix for local machine access is a logical extension in my books.
Do we agree at least that some form of multicast is the logical solution
to the case of one sender/many listeners?
Thanks for your thoughts,
Chris
--
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: cfriesen@xxxxxxxxxxxxxxxxxx
|