DragonFly On-Line Manual Pages

BW_MEM(8)                           LMBENCH                          BW_MEM(8)

NAME
       bw_mem - time memory bandwidth

SYNOPSIS
       bw_mem_cp [ -P <parallelism> ] [ -W <warmups> ] [ -N <repetitions> ]
       size rd|wr|rdwr|cp|fwr|frd|bzero|bcopy [align]

DESCRIPTION
       bw_mem allocates twice the specified amount of memory, zeros it, and
       then times the copying of the first half to the second half.  Results
       are reported in megabytes moved per second.

       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

       There are nine different memory benchmarks in bw_mem.  They each
       measure slightly different methods for reading, writing or copying
       data.

       rd     measures the time to read data into the processor.  It computes
              the sum of an array of integer values.  It accesses every fourth
              word.

       wr     measures the time to write data to memory.  It assigns a
              constant value to each memory of an array of integer values.  It
              accesses every fourth word.

       rdwr   measures the time to read data into memory and then write data
              to the same memory location.  For each element in an array it
              adds the current value to a running sum before assigning a new
              (constant) value to the element.  It accesses every fourth word.

       cp     measures the time to copy data from one location to another.  It
              does an array copy: dest[i] = source[i].  It accesses every
              fourth word.

       frd    measures the time to read data into the processor.  It computes
              the sum of an array of integer values.

       fwr    measures the time to write data to memory.  It assigns a
              constant value to each memory of an array of integer values.

       fcp    measures the time to copy data from one location to another.  It
              does an array copy: dest[i] = source[i].

       bzero  measures how fast the system can bzero memory.

       bcopy  measures how fast the system can bcopy data.

MEMORY UTILIZATION
       This benchmark can move up to three times the requested memory.  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'').

SEE ALSO
       lmbench(8).

AUTHOR
       Carl Staelin and Larry McVoy

       Comments, suggestions, and bug reports are always welcome.

(c)1994-2000 Larry McVoy and Carl Staelin
                                    $Date$                           BW_MEM(8)