Re: [PATCH v2] perf stat: Introduce skippable evsels

From: Ian Rogers
Date: Fri Apr 14 2023 - 19:04:15 EST

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On Fri, Apr 14, 2023 at 11:07 AM Liang, Kan <kan.liang@xxxxxxxxxxxxxxx> wrote:
>
>
>
> On 2023-04-14 1:19 a.m., Ian Rogers wrote:
> > 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%)
>
> Multiplexing?
>
> Thanks,
> Kan

I may have been running a test in the background otherwise I can't
explain it. Repeating the test yields no multiplexing:

```
$ perf stat true

Performance counter stats for 'true':

0.78 msec task-clock:u # 0.383
CPUs utilized
0 context-switches:u # 0.000
/sec
0 cpu-migrations:u # 0.000
/sec
47 page-faults:u # 60.174
K/sec
233,420 cycles:u # 0.299 GHz
133,318 instructions:u # 0.57
insn per cycle
31,396 branches:u # 40.196
M/sec
2,334 branch-misses:u # 7.43% of
all branches
1,167,100 TOPDOWN.SLOTS:u # 12.2 %
tma_retiring
# 28.9 %
tma_backend_bound
# 41.0 %
tma_frontend_bound
# 18.0 %
tma_bad_speculation
141,882 topdown-retiring:u
480,570 topdown-fe-bound:u
320,380 topdown-be-bound:u
224,266 topdown-bad-spec:u
2,173 INT_MISC.UOP_DROPPING:u # 2.782
M/sec
3,323 cpu/INT_MISC.RECOVERY_CYCLES,cmask=1,edge/u #
4.254 M/sec

0.002036744 seconds time elapsed

0.002252000 seconds user
0.000000000 seconds sys
```

Thanks,
Ian

> > 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.

Next message: Kelvin.Cao: "Re: [PATCH v2 1/1] dmaengine: switchtec-dma: Introduce Switchtec DMA engine PCI driver"
Previous message: Marijn Suijten: "Re: [PATCH v3] drm/msm/dpu: always program DSC active bits"
In reply to: Liang, Kan: "Re: [PATCH v2] perf stat: Introduce skippable evsels"
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