perf stat: Introduce skippable evsels

'perf stat' with no arguments will use default events and metrics. These
events may fail to open even with kernel and hypervisor disabled. When
these fail then the permissions error appears even though they were
implicitly selected. This is particularly a problem with the automatic
selection of the TopdownL1 metric group on certain architectures like
Skylake:

  $ perf stat true
  Error:
  Access to performance monitoring and observability operations is limited.
  Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open
  access to performance monitoring and observability operations for processes
  without CAP_PERFMON, CAP_SYS_PTRACE or CAP_SYS_ADMIN Linux capability.
  More information can be found at 'Perf events and tool security' document:
  https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html
  perf_event_paranoid setting 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 raw and ftrace function tracepoint access
  >= 1: Disallow CPU event access
  >= 2: Disallow kernel profiling
  To make the adjusted perf_event_paranoid setting permanent preserve it
  in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)
  $

This patch adds skippable evsels that when they fail to open won't cause
termination and will appear as "<not supported>" in output. The
TopdownL1 events, from the metric group, are marked as skippable. This
turns the failure above to:

  $ perf stat perf bench internals synthesize
  Computing performance of single threaded perf event synthesis by
  synthesizing events on the perf process itself:
    Average synthesis took: 49.287 usec (+- 0.083 usec)
    Average num. events: 3.000 (+- 0.000)
    Average time per event 16.429 usec
    Average data synthesis took: 49.641 usec (+- 0.085 usec)
    Average num. events: 11.000 (+- 0.000)
    Average time per event 4.513 usec

   Performance counter stats for 'perf bench internals synthesize':

            1,222.38 msec task-clock:u                     #    0.993 CPUs utilized
                   0      context-switches:u               #    0.000 /sec
                   0      cpu-migrations:u                 #    0.000 /sec
                 162      page-faults:u                    #  132.529 /sec
         774,445,184      cycles:u                         #    0.634 GHz                         (49.61%)
       1,640,969,811      instructions:u                   #    2.12  insn per cycle              (59.67%)
         302,052,148      branches:u                       #  247.102 M/sec                       (59.69%)
           1,807,718      branch-misses:u                  #    0.60% of all branches             (59.68%)
           5,218,927      CPU_CLK_UNHALTED.REF_XCLK:u      #    4.269 M/sec
                                                    #     17.3 %  tma_frontend_bound
                                                    #     56.4 %  tma_retiring
                                                    #      nan %  tma_backend_bound
                                                    #      nan %  tma_bad_speculation      (60.01%)
         536,580,469      IDQ_UOPS_NOT_DELIVERED.CORE:u    #  438.965 M/sec                       (60.33%)
     <not supported>      INT_MISC.RECOVERY_CYCLES_ANY:u
           5,223,936      CPU_CLK_UNHALTED.ONE_THREAD_ACTIVE:u #    4.274 M/sec                       (40.31%)
         774,127,250      CPU_CLK_UNHALTED.THREAD:u        #  633.297 M/sec                       (50.34%)
       1,746,579,518      UOPS_RETIRED.RETIRE_SLOTS:u      #    1.429 G/sec                       (50.12%)
       1,940,625,702      UOPS_ISSUED.ANY:u                #    1.588 G/sec                       (49.70%)

         1.231055525 seconds time elapsed

         0.258327000 seconds user
         0.965749000 seconds sys
  $

The event INT_MISC.RECOVERY_CYCLES_ANY:u is skipped as it can't be
opened with paranoia 2 on Skylake. With a lower paranoia, or as root,
all events/metrics are computed.

Signed-off-by: Ian Rogers <[email protected]>
Tested-by: Kan Liang <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Ahmad Yasin <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Athira Rajeev <[email protected]>
Cc: Caleb Biggers <[email protected]>
Cc: Edward Baker <[email protected]>
Cc: Florian Fischer <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Garry <[email protected]>
Cc: Kajol Jain <[email protected]>
Cc: Kang Minchul <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Perry Taylor <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Samantha Alt <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Sumanth Korikkar <[email protected]>
Cc: Suzuki Poulouse <[email protected]>
Cc: Thomas Richter <[email protected]>
Cc: Tiezhu Yang <[email protected]>
Cc: Weilin Wang <[email protected]>
Cc: Xing Zhengjun <[email protected]>
Cc: Yang Jihong <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: captain5050

tools/perf/builtin-stat.c

@@ -667,6 +667,13 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
 			evsel_list->core.threads->err_thread = -1;
 			return COUNTER_RETRY;
 		}
+	} else if (counter->skippable) {
+		if (verbose > 0)
+			ui__warning("skipping event %s that kernel failed to open .\n",
+				    evsel__name(counter));
+		counter->supported = false;
+		counter->errored = true;
+		return COUNTER_SKIP;
 	}
 
 	evsel__open_strerror(counter, &target, errno, msg, sizeof(msg));
@@ -1890,15 +1897,28 @@ static int add_default_attributes(void)
 		 * caused by exposing latent bugs. This is fixed properly in:
 		 * https://lore.kernel.org/lkml/[email protected]/
 		 */
-		if (metricgroup__has_metric("TopdownL1") && !perf_pmu__has_hybrid() &&
-		    metricgroup__parse_groups(evsel_list, "TopdownL1",
-					    /*metric_no_group=*/false,
-					    /*metric_no_merge=*/false,
-					    /*metric_no_threshold=*/true,
-					    stat_config.user_requested_cpu_list,
-					    stat_config.system_wide,
-					    &stat_config.metric_events) < 0)
-			return -1;
+		if (metricgroup__has_metric("TopdownL1") && !perf_pmu__has_hybrid()) {
+			struct evlist *metric_evlist = evlist__new();
+			struct evsel *metric_evsel;
+
+			if (!metric_evlist)
+				return -1;
+
+			if (metricgroup__parse_groups(metric_evlist, "TopdownL1",
+							/*metric_no_group=*/false,
+							/*metric_no_merge=*/false,
+							/*metric_no_threshold=*/true,
+							stat_config.user_requested_cpu_list,
+							stat_config.system_wide,
+							&stat_config.metric_events) < 0)
+				return -1;
+
+			evlist__for_each_entry(metric_evlist, metric_evsel) {
+				metric_evsel->skippable = true;
+			}
+			evlist__splice_list_tail(evsel_list, &metric_evlist->core.entries);
+			evlist__delete(metric_evlist);
+		}
 
 		/* Platform specific attrs */
 		if (evlist__add_default_attrs(evsel_list, default_null_attrs) < 0)

tools/perf/util/evsel.c

@@ -290,6 +290,7 @@ void evsel__init(struct evsel *evsel,
 	evsel->per_pkg_mask  = NULL;
 	evsel->collect_stat  = false;
 	evsel->pmu_name      = NULL;
+	evsel->skippable     = false;
 }
 
 struct evsel *evsel__new_idx(struct perf_event_attr *attr, int idx)
@@ -1725,9 +1726,13 @@ static int get_group_fd(struct evsel *evsel, int cpu_map_idx, int thread)
 		return -1;
 
 	fd = FD(leader, cpu_map_idx, thread);
-	BUG_ON(fd == -1);
+	BUG_ON(fd == -1 && !leader->skippable);
 
-	return fd;
+	/*
+	 * When the leader has been skipped, return -2 to distinguish from no
+	 * group leader case.
+	 */
+	return fd == -1 ? -2 : fd;
 }
 
 static void evsel__remove_fd(struct evsel *pos, int nr_cpus, int nr_threads, int thread_idx)
@@ -2109,6 +2114,12 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 
 			group_fd = get_group_fd(evsel, idx, thread);
 
+			if (group_fd == -2) {
+				pr_debug("broken group leader for %s\n", evsel->name);
+				err = -EINVAL;
+				goto out_close;
+			}
+
 			test_attr__ready();
 
 			/* Debug message used by test scripts */

tools/perf/util/evsel.h

@@ -95,6 +95,7 @@ struct evsel {
 		bool			weak_group;
 		bool			bpf_counter;
 		bool			use_config_name;
+		bool			skippable;
 		int			bpf_fd;
 		struct bpf_object	*bpf_obj;
 		struct list_head	config_terms;