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BW_PIPE(8)                          LMBENCH                         BW_PIPE(8)

NAME
       bw_pipe - time data movement through pipes

SYNOPSIS
       bw_pipe [ -m <message size> ] [ -M <total bytes> ] [ -P <parallelism> ]
       [ -W <warmups> ] [ -N <repetitions> ]

DESCRIPTION
       bw_pipe creates a Unix pipe between two processes and moves total bytes
       through the pipe in message size chunks (note that pipes are typically
       sized smaller than that).  The default total bytes is 10MB and the
       default message size is 64KB.

OUTPUT
       Output format is "Pipe bandwidth: %0.2f MB/sec\n",
       megabytes_per_second, i.e.,

       Pipe bandwidth: 4.87 MB/sec

MEMORY UTILIZATION
       This benchmark can move up to six times the requested memory per
       process.  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.

SEE ALSO
       lmbench(8).

AUTHOR
       Carl Staelin and Larry McVoy

       Comments, suggestions, and bug reports are always welcome.

(c)1994 Larry McVoy                 $Date$                          BW_PIPE(8)