BW_FILE_RD(8) - Linux man page online | Administration and privileged commands
Time the reading and summing of a file.
BW_FILE_RD(8) LMBENCH BW_FILE_RD(8)
(c)1994 Larry McVoy $Date$ BW_FILE_RD(8)
NAMEbw_file_rd - time the reading and summing of a file
SYNOPSISbw_file_rd [ -P <parallelism> ] [ -W <warmups> ] [ -N <repetitions> ] size file
DESCRIPTIONbw_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 sys‐ tems 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).
OUTPUTOutput format is "%0.2f %.2f\n", megabytes, megabytes_per_second, i.e., 8.00 25.33
MEMORY UTILIZATIONThis benchmark can move up to three times the requested memory. Most Unix systems imple‐ ment 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 des‐ tionation. 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 proces‐ sor architecture implemented ``load cache line'' and ``store cache line'' instructions (as well as ``getcachelinesize'').
ACKNOWLEDGEMENTFunding for the development of this tool was provided by Sun Microsystems Computer Corpo‐ ration.
AUTHORCarl Staelin and Larry McVoy Comments, suggestions, and bug reports are always welcome.
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|refer to||lmbench(8) | lmdd(8)|