NAME

       dispatch_benchmark — Measures block execution time

SYNOPSIS

       #include <dispatch/dispatch.h>

       uint64_t
       dispatch_benchmark(size_t count, void (^block)(void));

       uint64_t
       dispatch_benchmark_f(size_t count, void *context, void (*function)(void *));

DESCRIPTION

       The dispatch_benchmark() function executes the given block multiple times according to the count variable
       and  then  returns  the  average number of nanoseconds per execution.  This function is for debugging and
       performance analysis work.  For the best results, pass a high count value to dispatch_benchmark().   When
       benchmarking  concurrent  code,  please  compare  the  serial  version of the code against the concurrent
       version, and compare the concurrent version on different classes of hardware.  Please look for inflection
       points with various data sets and keep the following facts in mind:

             •   Code bound by computational bandwidth may be inferred by proportional changes in performance as
                 concurrency is increased.
             •   Code bound by memory bandwidth  may  be  inferred  by  negligible  changes  in  performance  as
                 concurrency is increased.
             •   Code  bound  by  critical  sections  may  be  inferred  by retrograde changes in performance as
                 concurrency is increased.
                       •   Intentional: locks, mutexes, and condition variables.
                       •   Accidental: unrelated and frequently modified data on the same cache-line.

RETURN VALUE

       The dispatch_benchmark() function returns the average number of nanoseconds  the  given  block  takes  to
       execute.

SEE ALSO

       dispatch(3)

Darwin                                             May 1, 2009                             dispatch_benchmark(3)