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Date: Mon, 17 Apr 2023 09:58:35 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Florian Fischer <florian.fischer@...q.space>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf stat: Introduce skippable evsels
On 2023-04-14 7:03 p.m., Ian Rogers wrote:
> On Fri, Apr 14, 2023 at 11:07 AM Liang, Kan <kan.liang@...ux.intel.com> 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:
The above multiplexing should be on a Skylake (since there is no
topdownL1 printed), but the test which you repeat seems on a Tigerlake
(has topdownL1). Could you please double check on a Skylake?
Thanks,
Kan
>
> ```
> $ 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@...gle.com>
>>> ---
>>> 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.
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