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

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 <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-stat.c

···
                                 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));

tools/perf/util/evsel.c

···
 		goto fallback_missing_features;
 	}
 out_close:
+	if (err)
+		threads->err_thread = thread;
+
 	do {
 		while (--thread >= 0) {
 			close(FD(evsel, cpu, thread));

tools/perf/util/thread_map.c

···
 	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)

tools/perf/util/thread_map.h

···
 struct thread_map {
 	refcount_t refcnt;
 	int nr;
+	int err_thread;
 	struct thread_map_data map[];
 };