NAME

       bw_file_rd - time the reading and summing of a file

SYNOPSIS

       bw_file_rd [ -P <parallelism> ] [ -W <warmups> ] [ -N <repetitions> ] size file

DESCRIPTION

       bw_file_rd  times the read of the specified file in 64KB blocks. Each block is summed up as a seried of 4
       byte integers in an unrolled loop.  Results are reported in megabytes read per second.

       The data is not accessed in the user  program;  the  benchmark  relies  on  the  operating  systems  read
       interface to have actually moved the data.  Systems that implement page flipping may fool this benchmark.

       The  benchmark  is  intended  to  be  used  on  a file that is in memory, i.e., the benchmark is a reread
       benchmark.  Other file benchmarking can be done with lmdd(8).

       The size specification may end with ``k'' or ``m'' to mean kilobytes (* 1024)  or  megabytes  (*  1024  *
       1024).

OUTPUT

       Output format is "%0.2f %.2f\n", megabytes, megabytes_per_second, i.e.,

       8.00 25.33

MEMORY UTILIZATION

       This  benchmark  can  move  up to three times the requested memory.  Most Unix systems implement the read
       system call as a bcopy from kernel space to 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_FILE_RD(8)