[PATCH v2] perf stat: Introduce skippable evsels
From: Ian Rogers
Date: Fri Apr 14 2023 - 01:19:42 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
fail and won't appear in output. The TopdownL1 events, from the metric
group, are marked as skippable. This turns the failure above to:
```
$ perf stat true
Performance counter stats for 'true':
1.26 msec task-clock:u # 0.328 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
49 page-faults:u # 38.930 K/sec
176,449 cycles:u # 0.140 GHz (48.99%)
122,905 instructions:u # 0.70 insn per cycle
28,264 branches:u # 22.456 M/sec
2,405 branch-misses:u # 8.51% of all branches
0.003834565 seconds time elapsed
0.000000000 seconds user
0.004130000 seconds sys
```
When the events can have kernel/hypervisor disabled, like on
Tigerlake, then it continues to succeed as:
```
$ perf stat true
Performance counter stats for 'true':
0.57 msec task-clock:u # 0.385 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
47 page-faults:u # 82.329 K/sec
287,017 cycles:u # 0.503 GHz
133,318 instructions:u # 0.46 insn per cycle
31,396 branches:u # 54.996 M/sec
2,442 branch-misses:u # 7.78% of all branches
998,790 TOPDOWN.SLOTS:u # 14.5 % tma_retiring
# 27.6 % tma_backend_bound
# 40.9 % tma_frontend_bound
# 17.0 % tma_bad_speculation
144,922 topdown-retiring:u
411,266 topdown-fe-bound:u
258,510 topdown-be-bound:u
184,090 topdown-bad-spec:u
2,585 INT_MISC.UOP_DROPPING:u # 4.528 M/sec
3,434 cpu/INT_MISC.RECOVERY_CYCLES,cmask=1,edge/u # 6.015 M/sec
0.001480954 seconds time elapsed
0.000000000 seconds user
0.001686000 seconds sys
```
And this likewise works if paranoia allows or running as root.
v2. Don't display the skipped events as <not counted> or <not supported>.
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
tools/perf/builtin-stat.c | 39 ++++++++++++++++++++++++++--------
tools/perf/util/evsel.c | 15 +++++++++++--
tools/perf/util/evsel.h | 1 +
tools/perf/util/stat-display.c | 4 ++++
4 files changed, 48 insertions(+), 11 deletions(-)
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index d3cbee7460fc..7a641a67486d 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));
@@ -1885,15 +1892,29 @@ static int add_default_attributes(void)
* Add TopdownL1 metrics if they exist. To minimize
* multiplexing, don't request threshold computation.
*/
- if (metricgroup__has_metric("TopdownL1") &&
- 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")) {
+ 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)
return -1;
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a85a987128aa..83a65f771666 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)
@@ -1720,9 +1721,13 @@ 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)
@@ -2104,6 +2109,12 @@ 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 68072ec655ce..98afe3351176 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;
diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index e6035ecbeee8..6b46bbb3d322 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -810,6 +810,10 @@ static bool should_skip_zero_counter(struct perf_stat_config *config,
struct perf_cpu cpu;
int idx;
+ /* Skip counters that were speculatively/default enabled rather than requested. */
+ if (counter->skippable)
+ return true;
+
/*
* Skip value 0 when enabling --per-thread globally,
* otherwise it will have too many 0 output.
--
2.40.0.634.g4ca3ef3211-goog