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Date: Sat, 6 Nov 2021 16:09:49 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Andi Kleen <ak@...ux.intel.com>,
Ian Rogers <irogers@...gle.com>,
Stephane Eranian <eranian@...gle.com>,
Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v4] perf evsel: Fix missing exclude_{host,guest} setting
Em Fri, Nov 05, 2021 at 01:58:47PM -0700, Namhyung Kim escreveu:
> The current logic for the perf missing feature has a bug that it can
> wrongly clear some modifiers like G or H. Actually some PMUs don't
> support any filtering or exclusion while others do. But we check it
> as a global feature.
>
> For example, the cycles event can have 'G' modifier to enable it only
> in the guest mode on x86. When you don't run any VMs it'll return 0.
>
> # perf stat -a -e cycles:G sleep 1
>
> Performance counter stats for 'system wide':
>
> 0 cycles:G
>
> 1.000721670 seconds time elapsed
>
> But when it's used with other pmu events that don't support G modifier,
> it'll be reset and return non-zero values.
>
> # perf stat -a -e cycles:G,msr/tsc/ sleep 1
>
> Performance counter stats for 'system wide':
>
> 538,029,960 cycles:G
> 16,924,010,738 msr/tsc/
>
> 1.001815327 seconds time elapsed
>
> This is because of the missing feature detection logic being global.
> Add a hashmap to set pmu-specific exclude_host/guest features.
⬢[acme@...lbox perf]$ perf test python
19: 'import perf' in python : FAILED!
⬢[acme@...lbox perf]$ perf test -v python
Couldn't bump rlimit(MEMLOCK), failures may take place when creating BPF maps, etc
19: 'import perf' in python :
--- start ---
test child forked, pid 11602
python usage test: "echo "import sys ; sys.path.append('/tmp/build/perf/python'); import perf" | '/usr/bin/python3' "
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: /tmp/build/perf/python/perf.cpython-39-x86_64-linux-gnu.so: undefined symbol: evsel__find_pmu
test child finished with -1
---- end ----
'import perf' in python: FAILED!
⬢[acme@...lbox perf]$
Trying to fix this now. please do a 'perf test' before submitting
patches.
- Arnaldo
> Reported-by: Stephane Eranian <eranian@...gle.com>
> Cc: Ravi Bangoria <ravi.bangoria@....com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> v4 changes)
> * add pmu->missing_features.exclude_guest
> * bail out if evsel->exclude_GH is set
>
> v3 changes)
> * check memory allocation failure
> * add more NULL check
>
> v2 changes)
> * change to enum perf_missing_pmu_features
> * pass NULL to hashmap__find() to skip checking
> * add a blank line after declaration
>
> tools/perf/util/evsel.c | 27 ++++++++++++++++++++++-----
> tools/perf/util/evsel.h | 4 ++++
> tools/perf/util/pmu.h | 4 ++++
> 3 files changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 2cfc2935d1d2..3cc1f8fcf15c 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1824,7 +1824,7 @@ static void evsel__disable_missing_features(struct evsel *evsel)
> evsel->open_flags &= ~(unsigned long)PERF_FLAG_FD_CLOEXEC;
> if (perf_missing_features.mmap2)
> evsel->core.attr.mmap2 = 0;
> - if (perf_missing_features.exclude_guest)
> + if (evsel->pmu && evsel->pmu->missing_features.exclude_guest)
> evsel->core.attr.exclude_guest = evsel->core.attr.exclude_host = 0;
> if (perf_missing_features.lbr_flags)
> evsel->core.attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
> @@ -1917,10 +1917,27 @@ bool evsel__detect_missing_features(struct evsel *evsel)
> perf_missing_features.mmap2 = true;
> pr_debug2_peo("switching off mmap2\n");
> return true;
> - } else if (!perf_missing_features.exclude_guest &&
> - (evsel->core.attr.exclude_guest || evsel->core.attr.exclude_host)) {
> - perf_missing_features.exclude_guest = true;
> - pr_debug2_peo("switching off exclude_guest, exclude_host\n");
> + } else if ((evsel->core.attr.exclude_guest || evsel->core.attr.exclude_host) &&
> + (evsel->pmu == NULL || evsel->pmu->missing_features.exclude_guest)) {
> + if (evsel->pmu == NULL) {
> + evsel->pmu = evsel__find_pmu(evsel);
> + if (evsel->pmu)
> + evsel->pmu->missing_features.exclude_guest = true;
> + else {
> + /* we cannot find PMU, disable attrs now */
> + evsel->core.attr.exclude_host = false;
> + evsel->core.attr.exclude_guest = false;
> + }
> + }
> +
> + if (evsel->exclude_GH) {
> + pr_debug2_peo("PMU has no exclude_host/guest support, bailing out\n");
> + return false;
> + }
> + if (!perf_missing_features.exclude_guest) {
> + perf_missing_features.exclude_guest = true;
> + pr_debug2_peo("switching off exclude_guest, exclude_host\n");
> + }
> return true;
> } else if (!perf_missing_features.sample_id_all) {
> perf_missing_features.sample_id_all = true;
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 846c827934de..dcc87c2881b8 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -22,6 +22,7 @@ struct target;
> struct hashmap;
> struct bperf_leader_bpf;
> struct bperf_follower_bpf;
> +struct perf_pmu;
>
> typedef int (evsel__sb_cb_t)(union perf_event *event, void *data);
>
> @@ -153,6 +154,9 @@ struct evsel {
> };
> unsigned long open_flags;
> int precise_ip_original;
> +
> + /* for missing_features */
> + struct perf_pmu *pmu;
> };
>
> struct perf_missing_features {
> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> index 15bbec3a9959..541889fa9f9c 100644
> --- a/tools/perf/util/pmu.h
> +++ b/tools/perf/util/pmu.h
> @@ -49,6 +49,10 @@ struct perf_pmu {
> struct list_head caps; /* HEAD struct perf_pmu_caps -> list */
> struct list_head list; /* ELEM */
> struct list_head hybrid_list;
> +
> + struct {
> + bool exclude_guest;
> + } missing_features;
> };
>
> extern struct perf_pmu perf_pmu__fake;
> --
> 2.34.0.rc0.344.g81b53c2807-goog
--
- Arnaldo
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