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line

NAME

line - cache line size

SYNOPSIS

line [ -M <len> ] [ -W <warmups> ] [ -N <repetitions> ]

DESCRIPTION

line tries to determine the cache line size in bytes of the largest cache which is smaller than len bytes.

line creates pointer chains which access the first word on each cache line on a page (randomly meandering through all the lines in a page before jumping to the next page). It measures the average memory latency for a variety of line sizes, starting with a line size of one word. When it finds an increase in the average latency that is significantly larger than the latency for the smaller line size then it assumes that it has found the line size.

This algorithm works because for line sizes less than the true line size, at least two line cache lines fit in the space of a true cache line. Since that cache line will be accessed twice, the first access will cause an expensive cache miss, while the second access will be a cache hit. Once the line cache line is equal to the true cache line size, then all accesses will cause cache misses.

BUGS

line is an experimental benchmark, but it seems to work well on most systems.

SEE ALSO

lmbench(8), tlb(8), cache(8), par_mem(8).

AUTHOR

Carl Staelin and Larry McVoy

Comments, suggestions, and bug reports are always welcome.