[PATCH v3 03/46] perf stat: Introduce skippable evsels
From: Ian Rogers
Date: Sat Apr 29 2023 - 01:35:59 EST
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 <irogers@xxxxxxxxxx>
---
tools/perf/builtin-stat.c | 38 +++++++++++++++++++++++++++++---------
tools/perf/util/evsel.c | 15 +++++++++++++--
tools/perf/util/evsel.h | 1 +
3 files changed, 43 insertions(+), 11 deletions(-)
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index be9677aa642f..ffb47b166098 100644
--- a/tools/perf/builtin-stat.c
+++ b/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/bff481ba-e60a-763f-0aa0-3ee53302c480@xxxxxxxxxxxxxxx/
*/
- 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)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 356c07f03be6..1cd04b5998d2 100644
--- a/tools/perf/util/evsel.c
+++ b/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 */
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 35805dcdb1b9..bf8f01af1c0b 100644
--- a/tools/perf/util/evsel.h
+++ b/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;
--
2.40.1.495.gc816e09b53d-goog