bw_file_rd - time the reading and summing of a file
[ -P <parallelism>
] [ -W <warmups>
] [ -N <repetitions>
] size file
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
The size specification may end with ``k'' or ``m'' to mean kilobytes (* 1024) or
megabytes (* 1024 * 1024).
Output format is "%0.2f %.2f\n", megabytes,
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
Funding for the development of this tool was provided by Sun Microsystems
Carl Staelin and Larry McVoy
Comments, suggestions, and bug reports are always welcome.