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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 band-
       width: there is one read	from the source	and a write to	the  destiona-
       tion.   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	``get-
       cachelinesize'').

ACKNOWLEDGEMENT
       Funding	for the	development of this tool was provided by Sun Microsys-
       tems 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)

NAME | SYNOPSIS | DESCRIPTION | OUTPUT | MEMORY UTILIZATION | ACKNOWLEDGEMENT | SEE ALSO | AUTHOR

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