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Message-ID: <77dd1ab3-9c94-c04a-24de-f8c192a6c8d2@linux.intel.com>
Date: Thu, 27 Apr 2023 14:52:46 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Ahmad Yasin <ahmad.yasin@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Stephane Eranian <eranian@...gle.com>,
Andi Kleen <ak@...ux.intel.com>,
Perry Taylor <perry.taylor@...el.com>,
Samantha Alt <samantha.alt@...el.com>,
Caleb Biggers <caleb.biggers@...el.com>,
Weilin Wang <weilin.wang@...el.com>,
Edward Baker <edward.baker@...el.com>,
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>,
Rob Herring <robh@...nel.org>,
Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
John Garry <john.g.garry@...cle.com>,
Kajol Jain <kjain@...ux.ibm.com>,
Sumanth Korikkar <sumanthk@...ux.ibm.com>,
Thomas Richter <tmricht@...ux.ibm.com>,
Tiezhu Yang <yangtiezhu@...ngson.cn>,
Ravi Bangoria <ravi.bangoria@....com>,
Leo Yan <leo.yan@...aro.org>,
Yang Jihong <yangjihong1@...wei.com>,
James Clark <james.clark@....com>,
Suzuki Poulouse <suzuki.poulose@....com>,
Kang Minchul <tegongkang@...il.com>,
Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 01/40] perf stat: Introduce skippable evsels
On 2023-04-26 3:00 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%)
> 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
> ```
If the same command runs with root permission, a different output will
be displayed as below:
$ sudo ./perf stat sleep 1
Performance counter stats for 'sleep 1':
0.97 msec task-clock # 0.001 CPUs
utilized
1 context-switches # 1.030 K/sec
0 cpu-migrations # 0.000 /sec
67 page-faults # 69.043 K/sec
1,135,552 cycles # 1.170 GHz
(50.51%)
1,126,446 instructions # 0.99 insn
per cycle
252,904 branches # 260.615 M/sec
7,297 branch-misses # 2.89% of
all branches
22,518 CPU_CLK_UNHALTED.REF_XCLK # 23.205
M/sec
56,994 INT_MISC.RECOVERY_CYCLES_ANY # 58.732 M/sec
The last two events are useless.
It's not reliable to rely on perf_event_open()/kernel to tell whether
an event is available or skippable. Kernel wouldn't check a specific event.
The patch works for the non-root mode is just because the event requires
root permission. It's rejected by the kernel because of lacking
permission. But if the same command runs with root privileges, the trash
events are printed as above.
I think a better way is to check the HW capability and decided whether
to append the TopdownL1 metrics.
https://lore.kernel.org/lkml/20230427182906.3411695-1-kan.liang@linux.intel.com/
Thanks,
Kan
>
> 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.
>
> 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 efda63f6bf32..eb34f5418ad3 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 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;
> 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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