[PATCH 6/8] perf tools: Probe for precise_ip with simple attr

[Jiri Olsa]

Currently we probe for precise_ip with user specified
perf_event_attr, which might fail because of unsupported
kernel features, which would get disabled during the
open time anyway.

Switching the probe to take place on simple hw cycles,
so the following record sets proper precise_ip:

  # perf record -e cycles:P ls
  # perf evlist -v
  cycles:P: size: 112, ... precise_ip: 3, ...

Link: http://lkml.kernel.org/n/tip-rwncfxifbhnmd89yx0va5zg0@xxxxxxxxxxxxxx
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/perf/util/evlist.c | 25 ++++++++++++++++++++-----
 tools/perf/util/evsel.c  |  8 --------
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 08cedb643ea6..ed20f4379956 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -230,18 +230,33 @@ void perf_evlist__set_leader(struct perf_evlist *evlist)
 	}
 }
 
-void perf_event_attr__set_max_precise_ip(struct perf_event_attr *attr)
+void perf_event_attr__set_max_precise_ip(struct perf_event_attr *pattr)
 {
-	attr->precise_ip = 3;
+	struct perf_event_attr attr = {
+		.type		= PERF_TYPE_HARDWARE,
+		.config		= PERF_COUNT_HW_CPU_CYCLES,
+		.exclude_kernel	= 1,
+		.precise_ip	= 3,
+	};
 
-	while (attr->precise_ip != 0) {
-		int fd = sys_perf_event_open(attr, 0, -1, -1, 0);
+	event_attr_init(&attr);
+
+	/*
+	 * Unnamed union member, not supported as struct member named
+	 * initializer in older compilers such as gcc 4.4.7
+	 */
+	attr.sample_period = 1;
+
+	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;
+		--attr.precise_ip;
 	}
+
+	pattr->precise_ip = attr.precise_ip;
 }
 
 int __perf_evlist__add_default(struct perf_evlist *evlist, bool precise)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index eec542bab815..2ef229e24b6f 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -294,20 +294,12 @@ struct perf_evsel *perf_evsel__new_cycles(bool precise)
 
 	if (!precise)
 		goto new_event;
-	/*
-	 * Unnamed union member, not supported as struct member named
-	 * initializer in older compilers such as gcc 4.4.7
-	 *
-	 * Just for probing the precise_ip:
-	 */
-	attr.sample_period = 1;
 
 	perf_event_attr__set_max_precise_ip(&attr);
 	/*
 	 * Now let the usual logic to set up the perf_event_attr defaults
 	 * to kick in when we return and before perf_evsel__open() is called.
 	 */
-	attr.sample_period = 0;
 new_event:
 	evsel = perf_evsel__new(&attr);
 	if (evsel == NULL)
-- 
2.17.2