Subject: Re: anyone ever done multicast AF_UNIX sockets?

From: Terje Eggestad <[email-masked]>
Date: 04 Mar 2003 00:38:02 +0100

The latency I belive, a 25% increase don't matter all that much. (
routinely send meesages sub micro second.  

that tcp BW is ridiculus low, make sure that you run with with good
sized socket buffers, and that tcp windowing is enabled.

But then again, if you want to send much data fast between processes, a
stream socket is a pretty bad idea anyway. 
A) shm
b) mmap a file, write into it, and send the filenake to the other side,
then mmap it there. 

Don't underestemate the BW of a fedex'ed  tape.

TJ

On Mon, 2003-03-03 at 22:32, Chris Friesen wrote:
    Terje Eggestad wrote:
    > On Mon, 2003-03-03 at 19:56, David S. Miller wrote:
    
    >     TCP bandwidth is slightly faster than AF_UNIX bandwidth on my
    >     sparc64 boxes for example.
    > 
    > I've seen that their are the same on linux.I tried to to do AF_UNIX
    > instead of AF_INET internally to boost perf, but to no avail. Makes you
    > suspect that the loopback device actually create an AF_UNIX connection
    > under the hood ;-)
    
    On my P4 1.8GHz, AF_INET vs AF_UNIX looks like this:

    *Local* Communication latencies in microseconds - smaller is better
    -------------------------------------------------------------
    Host           OS 2p/0K  Pipe AF     UDP  RPC/   TCP  RPC/ TCP
                       ctxsw       UNIX         UDP         TCP conn
    --------- ------- ----- ----- ---- ----- ----- ----- ----- ----
    pcard0ks. 2.4.18- 1.740  10.4 15.9  20.1  33.1  23.5  44.3 72.7
    pcard0ks. 2.4.18- 1.560  10.6 16.0  23.4  38.1  36.1  44.6 77.4

    *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
    --------- ------- ---- ---- ---- ------ ------ ------ ------ ---- -----
    pcard0ks. 2.4.18- 650. 677. 151.  721.9  958.0  290.8  288.8 955. 418.4
    pcard0ks. 2.4.18- 379. 701. 163.  714.8  949.5  289.5  288.5 956. 420.5

    On this machine at least, UDP latency is 25% worse than AF_UNIX, and TCP 
    bandwidth is about 22% that of AF_UNIX.
    
    Chris
    
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Terje Eggestad                  mailto:[email-masked]
Scali Scalable Linux Systems    http://www.scali.com

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