perf stat: Better report failure to collect system wide stats

Before:

[acme@doppio linux-2.6-tip]$ perf stat -a sleep 1s

 Performance counter stats for 'sleep 1s':

  <not counted>  task-clock-msecs
  <not counted>  context-switches
  <not counted>  CPU-migrations
  <not counted>  page-faults
  <not counted>  cycles
  <not counted>  instructions
  <not counted>  branches
  <not counted>  branch-misses
  <not counted>  cache-references
  <not counted>  cache-misses

    1.016998463  seconds time elapsed

[acme@doppio linux-2.6-tip]$

Now:

[acme@doppio linux-2.6-tip]$ perf stat -a sleep 1s
No permission to collect system-wide stats.
Consider tweaking /proc/sys/kernel/perf_event_paranoid.
[acme@doppio linux-2.6-tip]$

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1269274229-20442-4-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 28 insertions, 11 deletions

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index c92f90ff5a9f..1036ca739e6f 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -144,10 +144,11 @@ struct stats			runtime_branches_stats;
 #define ERR_PERF_OPEN \
 "Error: counter %d, sys_perf_event_open() syscall returned with %d (%s)\n"
 
-static void create_perf_stat_counter(int counter)
+static int create_perf_stat_counter(int counter)
 {
         struct perf_event_attr *attr = attrs + counter;
         int thread;
+        int ncreated = 0;
 
         if (scale)
                 attr->read_format = PERF_FORMAT_TOTAL_TIME_ENABLED |
@@ -159,9 +160,11 @@ static void create_perf_stat_counter(int counter)
                 for (cpu = 0; cpu < nr_cpus; cpu++) {
                         fd[cpu][counter][0] = sys_perf_event_open(attr,
                                         -1, cpumap[cpu], -1, 0);
-                        if (fd[cpu][counter][0] < 0 && verbose)
-                                fprintf(stderr, ERR_PERF_OPEN, counter,
-                                        fd[cpu][counter][0], strerror(errno));
+                        if (fd[cpu][counter][0] < 0)
+                                pr_debug(ERR_PERF_OPEN, counter,
+                                         fd[cpu][counter][0], strerror(errno));
+                        else
+                                ++ncreated;
                 }
         } else {
                 attr->inherit        = inherit;
@@ -172,12 +175,16 @@ static void create_perf_stat_counter(int counter)
                 for (thread = 0; thread < thread_num; thread++) {
                         fd[0][counter][thread] = sys_perf_event_open(attr,
                                 all_tids[thread], -1, -1, 0);
-                        if (fd[0][counter][thread] < 0 && verbose)
-                                fprintf(stderr, ERR_PERF_OPEN, counter,
-                                        fd[0][counter][thread],
-                                        strerror(errno));
+                        if (fd[0][counter][thread] < 0)
+                                pr_debug(ERR_PERF_OPEN, counter,
+                                         fd[0][counter][thread],
+                                         strerror(errno));
+                        else
+                                ++ncreated;
                 }
         }
+
+        return ncreated;
 }
 
 /*
@@ -264,7 +271,7 @@ static int run_perf_stat(int argc __used, const char **argv)
 {
         unsigned long long t0, t1;
         int status = 0;
-        int counter;
+        int counter, ncreated = 0;
         int child_ready_pipe[2], go_pipe[2];
         const bool forks = (argc > 0);
         char buf;
@@ -324,7 +331,16 @@ static int run_perf_stat(int argc __used, const char **argv)
         }
 
         for (counter = 0; counter < nr_counters; counter++)
-                create_perf_stat_counter(counter);
+                ncreated += create_perf_stat_counter(counter);
+
+        if (ncreated == 0) {
+                pr_err("No permission to collect %sstats.\n"
+                       "Consider tweaking /proc/sys/kernel/perf_event_paranoid.\n",
+                       system_wide ? "system-wide " : "");
+                if (child_pid != -1)
+                        kill(child_pid, SIGTERM);
+                return -1;
+        }
 
         /*
          * Enable counters and exec the command:
@@ -587,7 +603,8 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
                 status = run_perf_stat(argc, argv);
         }
 
-        print_stat(argc, argv);
+        if (status != -1)
+                print_stat(argc, argv);
 
         return status;
 }