libperf-counting(7)
|
===================
|
|
NAME
|
----
|
libperf-counting - counting interface
|
|
DESCRIPTION
|
-----------
|
The counting interface provides API to measure and get count for specific perf events.
|
|
The following test tries to explain count on `counting.c` example.
|
|
It is by no means complete guide to counting, but shows libperf basic API for counting.
|
|
The `counting.c` comes with libperf package and can be compiled and run like:
|
|
[source,bash]
|
--
|
$ gcc -o counting counting.c -lperf
|
$ sudo ./counting
|
count 176792, enabled 176944, run 176944
|
count 176242, enabled 176242, run 176242
|
--
|
|
It requires root access, because of the `PERF_COUNT_SW_CPU_CLOCK` event,
|
which is available only for root.
|
|
The `counting.c` example monitors two events on the current process and displays
|
their count, in a nutshell it:
|
|
* creates events
|
* adds them to the event list
|
* opens and enables events through the event list
|
* does some workload
|
* disables events
|
* reads and displays event counts
|
* destroys the event list
|
|
The first thing you need to do before using libperf is to call init function:
|
|
[source,c]
|
--
|
8 static int libperf_print(enum libperf_print_level level,
|
9 const char *fmt, va_list ap)
|
10 {
|
11 return vfprintf(stderr, fmt, ap);
|
12 }
|
|
14 int main(int argc, char **argv)
|
15 {
|
...
|
35 libperf_init(libperf_print);
|
--
|
|
It will setup the library and sets function for debug output from library.
|
|
The `libperf_print` callback will receive any message with its debug level,
|
defined as:
|
|
[source,c]
|
--
|
enum libperf_print_level {
|
LIBPERF_ERR,
|
LIBPERF_WARN,
|
LIBPERF_INFO,
|
LIBPERF_DEBUG,
|
LIBPERF_DEBUG2,
|
LIBPERF_DEBUG3,
|
};
|
--
|
|
Once the setup is complete we start by defining specific events using the `struct perf_event_attr`.
|
|
We create software events for cpu and task:
|
|
[source,c]
|
--
|
20 struct perf_event_attr attr1 = {
|
21 .type = PERF_TYPE_SOFTWARE,
|
22 .config = PERF_COUNT_SW_CPU_CLOCK,
|
23 .read_format = PERF_FORMAT_TOTAL_TIME_ENABLED|PERF_FORMAT_TOTAL_TIME_RUNNING,
|
24 .disabled = 1,
|
25 };
|
26 struct perf_event_attr attr2 = {
|
27 .type = PERF_TYPE_SOFTWARE,
|
28 .config = PERF_COUNT_SW_TASK_CLOCK,
|
29 .read_format = PERF_FORMAT_TOTAL_TIME_ENABLED|PERF_FORMAT_TOTAL_TIME_RUNNING,
|
30 .disabled = 1,
|
31 };
|
--
|
|
The `read_format` setup tells perf to include timing details together with each count.
|
|
Next step is to prepare threads map.
|
|
In this case we will monitor current process, so we create threads map with single pid (0):
|
|
[source,c]
|
--
|
37 threads = perf_thread_map__new_dummy();
|
38 if (!threads) {
|
39 fprintf(stderr, "failed to create threads\n");
|
40 return -1;
|
41 }
|
42
|
43 perf_thread_map__set_pid(threads, 0, 0);
|
--
|
|
Now we create libperf's event list, which will serve as holder for the events we want:
|
|
[source,c]
|
--
|
45 evlist = perf_evlist__new();
|
46 if (!evlist) {
|
47 fprintf(stderr, "failed to create evlist\n");
|
48 goto out_threads;
|
49 }
|
--
|
|
We create libperf's events for the attributes we defined earlier and add them to the list:
|
|
[source,c]
|
--
|
51 evsel = perf_evsel__new(&attr1);
|
52 if (!evsel) {
|
53 fprintf(stderr, "failed to create evsel1\n");
|
54 goto out_evlist;
|
55 }
|
56
|
57 perf_evlist__add(evlist, evsel);
|
58
|
59 evsel = perf_evsel__new(&attr2);
|
60 if (!evsel) {
|
61 fprintf(stderr, "failed to create evsel2\n");
|
62 goto out_evlist;
|
63 }
|
64
|
65 perf_evlist__add(evlist, evsel);
|
--
|
|
Configure event list with the thread map and open events:
|
|
[source,c]
|
--
|
67 perf_evlist__set_maps(evlist, NULL, threads);
|
68
|
69 err = perf_evlist__open(evlist);
|
70 if (err) {
|
71 fprintf(stderr, "failed to open evsel\n");
|
72 goto out_evlist;
|
73 }
|
--
|
|
Both events are created as disabled (note the `disabled = 1` assignment above),
|
so we need to enable the whole list explicitly (both events).
|
|
From this moment events are counting and we can do our workload.
|
|
When we are done we disable the events list.
|
|
[source,c]
|
--
|
75 perf_evlist__enable(evlist);
|
76
|
77 while (count--);
|
78
|
79 perf_evlist__disable(evlist);
|
--
|
|
Now we need to get the counts from events, following code iterates through the
|
events list and read counts:
|
|
[source,c]
|
--
|
81 perf_evlist__for_each_evsel(evlist, evsel) {
|
82 perf_evsel__read(evsel, 0, 0, &counts);
|
83 fprintf(stdout, "count %llu, enabled %llu, run %llu\n",
|
84 counts.val, counts.ena, counts.run);
|
85 }
|
--
|
|
And finally cleanup.
|
|
We close the whole events list (both events) and remove it together with the threads map:
|
|
[source,c]
|
--
|
87 perf_evlist__close(evlist);
|
88
|
89 out_evlist:
|
90 perf_evlist__delete(evlist);
|
91 out_threads:
|
92 perf_thread_map__put(threads);
|
93 return err;
|
94 }
|
--
|
|
REPORTING BUGS
|
--------------
|
Report bugs to <linux-perf-users@vger.kernel.org>.
|
|
LICENSE
|
-------
|
libperf is Free Software licensed under the GNU LGPL 2.1
|
|
RESOURCES
|
---------
|
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
|
|
SEE ALSO
|
--------
|
libperf(3), libperf-sampling(7)
|
