[PATCH] perf stat: Ignore error thread when enabling system-wide --per-thread

[Jin Yao]

If we execute 'perf stat --per-thread' with non-root account
(even set kernel.perf_event_paranoid = -1 yet), it reports the error:

jinyao@skl:~$ perf stat --per-thread
Error:
You may not have permission to collect system-wide stats.

Consider tweaking /proc/sys/kernel/perf_event_paranoid,
which controls use of the performance events system by
unprivileged users (without CAP_SYS_ADMIN).

The current value is 2:

  -1: Allow use of (almost) all events by all users
      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
>= 0: Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
      Disallow raw tracepoint access by users without CAP_SYS_ADMIN
>= 1: Disallow CPU event access by users without CAP_SYS_ADMIN
>= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN

To make this setting permanent, edit /etc/sysctl.conf too, e.g.:

        kernel.perf_event_paranoid = -1

Perhaps the ptrace rule doesn't allow to trace some processes. But anyway
the global --per-thread mode had better ignore such errors and continue
working on other threads.

This patch will record the index of error thread in perf_evsel__open()
and remove this thread before retrying.

For example (run with non-root, kernel.perf_event_paranoid isn't set):

jinyao@skl:~$ perf stat --per-thread
^C
 Performance counter stats for 'system wide':

          vmstat-3458               6.171984      cpu-clock:u (msec)        #    0.000 CPUs utilized
            perf-3670               0.515599      cpu-clock:u (msec)        #    0.000 CPUs utilized
          vmstat-3458              1,163,643      cycles:u                  #    0.189 GHz
            perf-3670                 40,881      cycles:u                  #    0.079 GHz
          vmstat-3458              1,410,238      instructions:u            #    1.21  insn per cycle
            perf-3670                  3,536      instructions:u            #    0.09  insn per cycle
          vmstat-3458                288,937      branches:u                #   46.814 M/sec
            perf-3670                    936      branches:u                #    1.815 M/sec
          vmstat-3458                 15,195      branch-misses:u           #    5.26% of all branches
            perf-3670                     76      branch-misses:u           #    8.12% of all branches

      12.651675247 seconds time elapsed

Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
---
 tools/perf/builtin-stat.c    | 14 +++++++++++++-
 tools/perf/util/evsel.c      |  3 +++
 tools/perf/util/thread_map.c |  1 +
 tools/perf/util/thread_map.h |  1 +
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 98bf9d3..bcdb47c 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -632,7 +632,19 @@ static int __run_perf_stat(int argc, const char **argv)
                                 if (verbose > 0)
                                         ui__warning("%s\n", msg);
                                 goto try_again;
-                        }
+			} else if (target__has_per_thread(&target) &&
+				   evsel_list->threads &&
+				   evsel_list->threads->err_thread != -1) {
+				/*
+				 * For global --per-thread case, skip current
+				 * error thread.
+				 */
+				if (!thread_map__remove(evsel_list->threads,
+							evsel_list->threads->err_thread)) {
+					evsel_list->threads->err_thread = -1;
+					goto try_again;
+				}
+			}
 
 			perf_evsel__open_strerror(counter, &target,
 						  errno, msg, sizeof(msg));
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a4d256e..12f8733 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1899,6 +1899,9 @@ int perf_evsel__open(struct perf_evsel *evsel, struct cpu_map *cpus,
 		goto fallback_missing_features;
 	}
 out_close:
+	if (err)
+		threads->err_thread = thread;
+
 	do {
 		while (--thread >= 0) {
 			close(FD(evsel, cpu, thread));
diff --git a/tools/perf/util/thread_map.c b/tools/perf/util/thread_map.c
index 3e1038f..870cb0c 100644
--- a/tools/perf/util/thread_map.c
+++ b/tools/perf/util/thread_map.c
@@ -32,6 +32,7 @@ static void thread_map__reset(struct thread_map *map, int start, int nr)
 	size_t size = (nr - start) * sizeof(map->map[0]);
 
 	memset(&map->map[start], 0, size);
+	map->err_thread = -1;
 }
 
 static struct thread_map *thread_map__realloc(struct thread_map *map, int nr)
diff --git a/tools/perf/util/thread_map.h b/tools/perf/util/thread_map.h
index 0a806b9..ac6baf1 100644
--- a/tools/perf/util/thread_map.h
+++ b/tools/perf/util/thread_map.h
@@ -14,6 +14,7 @@ struct thread_map_data {
 struct thread_map {
 	refcount_t refcnt;
 	int nr;
+	int err_thread;
 	struct thread_map_data map[];
 };
 
-- 
2.7.4