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(8)