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BW_TCP(1)                           LMBENCH                          BW_TCP(1)


NAME

       bw_tcp - time data movement through TCP/IP sockets


SYNOPSIS

       bw_tcp [ -m <message size> ] [ -M <total bytes> ] [ -P <parallelism> ]
       [ -W <warmups> ] [ -N <repetitions> ] server
       bw_tcp -s
       bw_tcp -S <server>


DESCRIPTION

       bw_tcp is a client/server program that moves data over a TCP/IP socket.
       Nothing is done with the data on either side; total bytes of data is
       moved in message size chunks.

       bw_tcp has three forms of usage: as a server (-s), as a client (bw_tcp
       localhost), and as a shutdown (bw_tcp -S localhost).

       The default amount of data is 10MB.  The client form may specify a
       different amount of data.  Specifications may end with ``k'' or ``m''
       to mean kilobytes (* 1024) or megabytes (* 1024 * 1024).


OUTPUT

       Output format is Socket bandwidth using localhost: 2.32 MB/sec


MEMORY UTILIZATION

       This benchmark can move up to six times the requested memory per
       process when run through the loopback device.  There are two processes,
       the sender and the receiver.  Most Unix systems implement the
       read/write system calls as a bcopy from/to kernel space to/from user
       space.  Bcopy will use 2-3 times as much memory bandwidth: there is one
       read from the source and a write to the destionation.  The write
       usually results in a cache line read and then a write back of the cache
       line at some later point.  Memory utilization might be reduced by 1/3
       if the processor architecture implemented "load cache line" and "store
       cache line" instructions (as well as getcachelinesize).


ACKNOWLEDGEMENT

       Funding for the development of this tool was provided by Sun
       Microsystems Computer Corporation and Silicon Graphics, Inc.


SEE ALSO

       lmbench(8).


AUTHOR

       Carl Staelin and Larry McVoy

       Comments, suggestions, and bug reports are always welcome.

(c)1994 Larry McVoy                 $Date$                           BW_TCP(1)

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