[tip:perf/core] perf evsel: Add a debug print if perf_event_open fails

[tip-bot for Adrian Hunter <tipbot@zytor.com>]

Commit-ID:  f852fd621ca19f557f2e3d05900366be7c7afb83
Gitweb:     http://git.kernel.org/tip/f852fd621ca19f557f2e3d05900366be7c7afb83
Author:     Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Fri, 1 Nov 2013 15:51:29 +0200
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Mon, 4 Nov 2013 12:18:17 -0300

perf evsel: Add a debug print if perf_event_open fails

There is a debug print (at verbose level 2) for each call to
perf_event_open.  Add another debug print if the call fails, and print
the error number.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1383313899-15987-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/evsel.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 3a334f0..f0e65de 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1051,6 +1051,8 @@ retry_open:
 								     group_fd, flags);
 			if (FD(evsel, cpu, thread) < 0) {
 				err = -errno;
+				pr_debug2("perf_event_open failed, error %d\n",
+					  err);
 				goto try_fallback;
 			}
 			set_rlimit = NO_CHANGE;