DragonFly On-Line Manual Pages

BW_FILE_RD(8)                       LMBENCH                      BW_FILE_RD(8)

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)