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1 .\" Copyright (c) 2008-2009 Apple Inc. All rights reserved.
2 .Dd May 1, 2009
3 .Dt dispatch_benchmark 3
4 .Os Darwin
5 .Sh NAME
6 .Nm dispatch_benchmark
7 .Nd Measures block execution time
8 .Sh SYNOPSIS
9 .Fd #include <dispatch/dispatch.h>
10 .Ft uint64_t
11 .Fo dispatch_benchmark
12 .Fa "size_t count" "void (^block)(void)"
13 .Fc
14 .Ft uint64_t
15 .Fo dispatch_benchmark_f
16 .Fa "size_t count" "void *context" "void (*function)(void *)"
17 .Fc
18 .Sh DESCRIPTION
19 The
20 .Fn dispatch_benchmark
21 function executes the given
22 .Fa block
23 multiple times according to the
24 .Fa count
25 variable and then returns the average number of nanoseconds per execution.
26 This function is for debugging and performance analysis work.
27 For the best
28 results, pass a high count value to
29 .Fn dispatch_benchmark .
30 When benchmarking concurrent code, please compare the
31 serial version of the code against the concurrent version, and compare the
32 concurrent version on different classes of hardware.
33 Please look for inflection
34 points with various data sets and keep the following facts in mind:
35 .Pp
36 .Bl -bullet -offset indent -compact
37 .It
38 Code bound by computational bandwidth may be inferred by proportional
39 changes in performance as concurrency is increased.
40 .It
41 Code bound by memory bandwidth may be inferred by negligible changes in
42 performance as concurrency is increased.
43 .It
44 Code bound by critical sections may be inferred by retrograde changes in
45 performance as concurrency is increased.
46 .Bl -bullet -offset indent -compact
47 .It
48 Intentional: locks, mutexes, and condition variables.
49 .It
50 Accidental: unrelated and frequently modified data on the same cache-line.
51 .El
52 .El
53 .Sh RETURN VALUE
54 The
55 .Fn dispatch_benchmark
56 function returns the average number of nanoseconds the given block takes to
57 execute.
58 .Sh SEE ALSO
59 .Xr dispatch 3