Provided by: lmbench_3.0-a9+debian.1-2_amd64 
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)