The single most important element of a good benchmarking system is
the quality and reliability of its measurement system.
lmbench's
timing subsystem manages the experimental timing process to produce
accurate results in the least possible time.
lmbench
includes methods for measuring and eliminating several factors that
influence the accuracy of timing measurements, such as the resolution
of the system clock.
lmbench
gets accurate results by considering clock resolution,
auto-sizing the duration of each benchmark, and conducting multiple
experiments.
measures the performance of
benchmark
repeatedly and reports the median result.
benchmp
creates
parallel
sub-processes which run
benchmark
in parallel. This allows lmbench to measure the system's ability to
scale as the number of client processes increases. Each sub-process
executes
initialize
before starting the benchmarking cycle. It will call
benchmark
several times in order to collect
repetitions
results. After all the benchmark results have been collected,
cleanup
is called to cleanup any resources which may have been allocated
by
initialize
or
benchmark .cookie
is a void pointer to a hunk of memory that can be used to store any
parameters or state that is needed by the benchmark.
void benchmp_getstate()
returns a void pointer to the lmbench-internal state used during
benchmarking. The state is not to be used or accessed directly
by clients, but rather would be passed into
benchmp_interval.
iter_t benchmp_interval(void* state)
returns the number of times the benchmark should execute its
benchmark loop during this timing interval. This is used only
for weird benchmarks which cannot implement the benchmark
body in a function which can return, such as the page fault
handler. Please see
lat_sig.c
for sample usage.
void start(struct timeval *begin)
starts a timing interval. If
begin
is non-null, save the start time in
begin .
stops a timing interval, returning the number of elapsed micro-seconds.
uint64 get_n()
returns the number of times
loop_body
was executed during the timing interval.
void set_n(uint64 n)
sets the number of times
loop_body
was executed during the timing interval.
uint64 gettime()
returns the number of micro-seconds in the timing interval.
void settime(uint64 u)
sets the number of micro-seconds in the timing interval.
uint64 get_enough(uint64 enough)
return the time in micro-seconds needed to accurately measure a timing
interval.
uint64 t_overhead()
return the time in micro-seconds needed to measure time.
double l_overhead()
return the time in micro-seconds needed to do a simple loop.
VARIABLES
There are three environment variables that can be used to modify
the
lmbench
timing subsystem: ENOUGH, TIMING_O, and LOOP_O.
The environment variables can be used to directly set the results
of
get_enough , t_overhead ,
and
l_overhead .
When running a large number of benchmarks, or repeating the same
benchmark many times, this can save time by eliminating the necessity
of recalculating these values for each run.