perf tests: Do not rely on dso__data_read_offset() to open dso

Do not rely on dso__data_read_offset() will always call dso__data_fd()
internally.  With multi-thread support, accessing a fd will be protected
by a lock and it'll cause a huge contention.  It can be avoided since we
can skip reading from file if there's a data in the dso cache.

If one needs to call the dso__data_read_offset(), [s]he also needs to
call dso__data_fd() (or set dso->binary_type at least) first like the
dwarf unwind code does.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1422585209-32742-2-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/dso-data.c

@@ -112,6 +112,9 @@ int test__dso_data(void)
 
 	dso = dso__new((const char *)file);
 
+	TEST_ASSERT_VAL("Failed to access to dso",
+			dso__data_fd(dso, &machine) >= 0);
+
 	/* Basic 10 bytes tests. */
 	for (i = 0; i < ARRAY_SIZE(offsets); i++) {
 		struct test_data_offset *data = &offsets[i];
@@ -252,13 +255,13 @@ int test__dso_data_cache(void)
 		struct dso *dso = dsos[i];
 
 		/*
-		 * Open dsos via dso__data_fd or dso__data_read_offset.
-		 * Both opens the data file and keep it open.
+		 * Open dsos via dso__data_fd(), it opens the data
+		 * file and keep it open (unless open file limit).
 		 */
-		if (i % 2) {
 		fd = dso__data_fd(dso, &machine);
 		TEST_ASSERT_VAL("failed to get fd", fd > 0);
-		} else {
+
+		if (i % 2) {
 			#define BUFSIZE 10
 			u8 buf[BUFSIZE];
 			ssize_t n;