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)