benchmp, benchmp_getstate, benchmp_interval, start, stop, get_n, set_n, gettime, settime, get_enough, t_overhead, l_overhead - the lmbench timing subsystem
typedef u_long iter_t;
typedef (*bench_f)(iter_t iterations, void* cookie);
typedef (*support_f)(iter_t iterations, void* cookie);
void benchmp(support_f initialize, bench_f benchmark, support_f cleanup, int enough, int parallel, int warmup, int repetitions, void* cookie);
iter_t benchmp_interval(void* state);
void start(struct timeval *begin);
void set_n(uint64 n);
void settime(uint64 u);
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, autosizing the duration of each benchmark, and conducting multiple experiments.
void benchmp(initialize, benchmark, cleanup, enough, parallel, warmup,
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 bench_mark . 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.
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 .
uint64 stop(struct timeval *begin, struct timeval *end) stops a timing interval, returning the number of elapsed microseconds.
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.
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.
return the time in micro-seconds needed to measure time.
return the time in micro-seconds needed to do a simple loop.
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.
Development of lmbench is continuing.
lmbench(8) , lmbench(3) , reporting(3) , results(3) .
Carl Staelin and Larry McVoy
Comments, suggestions, and bug reports are always welcome.
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