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Subject[PATCH 16/16] perf tools: By default use the most precise "cycles" hw counter available
Date
From: Arnaldo Carvalho de Melo <acme@redhat.com>

If the user doesn't specify any event, try the most precise "cycles"
available, i.e. start by "cycles:ppp" and go on removing "p" till it
works.

E.g.

$ perf record usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.017 MB perf.data (11 samples) ]
$ perf evlist
cycles:pp
$ perf evlist -v
cycles:pp: size: 112, { sample_period, sample_freq }: 4000, sample_type:
IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1,
enable_on_exec: 1, task: 1, precise_ip: 2, sample_id_all: 1,
exclude_guest: 1, mmap2: 1, comm_exec: 1
$ grep 'model name' /proc/cpuinfo | head -1
model name : Intel(R) Core(TM) i7-3667U CPU @ 2.00GHz
$

When 'cycles' appears explicitely is specified this will not be tried,
i.e. the user has full control of the level of precision to be used:

$ perf record -e cycles usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.016 MB perf.data (9 samples) ]
$ perf evlist
cycles
$ perf evlist -v
cycles: size: 112, { sample_period, sample_freq }: 4000, sample_type:
IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1,
enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2:
1, comm_exec: 1
$

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Chandler Carruth <chandlerc@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://www.youtube.com/watch?v=nXaxk27zwlk
Link: http://lkml.kernel.org/n/tip-b1ywebmt22pi78vjxau01wth@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/evlist.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 89546228b8ed..e7e195d867ea 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -205,6 +205,20 @@ void perf_evlist__set_leader(struct perf_evlist *evlist)
}
}

+static void perf_event_attr__set_max_precise_ip(struct perf_event_attr *attr)
+{
+ attr->precise_ip = 3;
+
+ while (attr->precise_ip != 0) {
+ int fd = sys_perf_event_open(attr, 0, -1, -1, 0);
+ if (fd != -1) {
+ close(fd);
+ break;
+ }
+ --attr->precise_ip;
+ }
+}
+
int perf_evlist__add_default(struct perf_evlist *evlist)
{
struct perf_event_attr attr = {
@@ -215,13 +229,15 @@ int perf_evlist__add_default(struct perf_evlist *evlist)

event_attr_init(&attr);

+ perf_event_attr__set_max_precise_ip(&attr);
+
evsel = perf_evsel__new(&attr);
if (evsel == NULL)
goto error;

- /* use strdup() because free(evsel) assumes name is allocated */
- evsel->name = strdup("cycles");
- if (!evsel->name)
+ /* use asprintf() because free(evsel) assumes name is allocated */
+ if (asprintf(&evsel->name, "cycles%.*s",
+ attr.precise_ip ? attr.precise_ip + 1 : 0, ":ppp") < 0)
goto error_free;

perf_evlist__add(evlist, evsel);
--
2.1.0


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