linux-kernel - [PATCH 10/10] perf stat: Fallback to user only counters when perf_event

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Date:	Thu, 12 May 2016 17:03:55 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andy Lutomirski <luto@...nel.org>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Wang Nan <wangnan0@...wei.com>
Subject: [PATCH 10/10] perf stat: Fallback to user only counters when perf_event_paranoid > 1

From: Arnaldo Carvalho de Melo <acme@...hat.com>

After 0161028b7c8a ("perf/core: Change the default paranoia level to 2")
'perf stat' fails for users without CAP_SYS_ADMIN, so just use
'perf_evsel__fallback()' to have the same behaviour as 'perf record',
i.e. set perf_event_attr.exclude_kernel to 1.

Now:

  [acme@...et linux]$ perf stat usleep 1

   Performance counter stats for 'usleep 1':

          0.352536      task-clock:u (msec)  #   0.423 CPUs utilized
                 0      context-switches:u   #   0.000 K/sec
                 0      cpu-migrations:u     #   0.000 K/sec
                49      page-faults:u        #   0.139 M/sec
           309,407      cycles:u             #   0.878 GHz
           243,791      instructions:u       #   0.79  insn per cycle
            49,622      branches:u           # 140.757 M/sec
             3,884      branch-misses:u      #   7.83% of all branches

       0.000834174 seconds time elapsed

  [acme@...et linux]$

Reported-by: Ingo Molnar <mingo@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: David Ahern <dsahern@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Wang Nan <wangnan0@...wei.com>
Link: http://lkml.kernel.org/n/tip-b20jmx4dxt5hpaa9t2rroi0o@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/builtin-stat.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 1f19f2f999c8..307e8a1a003c 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -528,6 +528,7 @@ static int __run_perf_stat(int argc, const char **argv)
 		perf_evlist__set_leader(evsel_list);
 
 	evlist__for_each(evsel_list, counter) {
+try_again:
 		if (create_perf_stat_counter(counter) < 0) {
 			/*
 			 * PPC returns ENXIO for HW counters until 2.6.37
@@ -544,7 +545,11 @@ static int __run_perf_stat(int argc, const char **argv)
 				if ((counter->leader != counter) ||
 				    !(counter->leader->nr_members > 1))
 					continue;
-			}
+			} else if (perf_evsel__fallback(counter, errno, msg, sizeof(msg))) {
+                                if (verbose)
+                                        ui__warning("%s\n", msg);
+                                goto try_again;
+                        }
 
 			perf_evsel__open_strerror(counter, &target,
 						  errno, msg, sizeof(msg));
-- 
2.5.5