Messages in this thread | | | From | Namhyung Kim <> | Date | Sun, 17 Oct 2021 21:44:28 -0700 | Subject | Re: [PATCH] perf evsel: Fix missing exclude_{host,guest} setting |
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Hi Jiri,
On Sun, Oct 17, 2021 at 12:06 PM Jiri Olsa <jolsa@redhat.com> wrote: > > On Fri, Oct 15, 2021 at 10:12:53PM -0700, Namhyung Kim wrote: > > 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. > > > > Reported-by: Stephane Eranian <eranian@google.com> > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> > > --- > > tools/perf/util/evsel.c | 47 +++++++++++++++++++++++++++++++++++------ > > tools/perf/util/evsel.h | 6 ++++++ > > 2 files changed, 47 insertions(+), 6 deletions(-) > > > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > > index dbfeceb2546c..437a28e769fe 100644 > > --- a/tools/perf/util/evsel.c > > +++ b/tools/perf/util/evsel.c > > @@ -1434,6 +1434,10 @@ void evsel__delete(struct evsel *evsel) > > { > > evsel__exit(evsel); > > free(evsel); > > + > > + /* just free it for the first evsel */ > > + hashmap__free(perf_missing_features.pmu); > > + perf_missing_features.pmu = NULL; > > } > > > > void evsel__compute_deltas(struct evsel *evsel, int cpu, int thread, > > @@ -1791,6 +1795,23 @@ static int __evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus, > > return 0; > > } > > > > +#define PMU_HASH_BITS 4 > > + > > +static size_t pmu_hash(const void *key, void *ctx __maybe_unused) > > +{ > > + const struct evsel *evsel = key; > > + > > + return hash_bits(evsel->core.attr.type, PMU_HASH_BITS); > > +} > > + > > +static bool pmu_equal(const void *key1, const void *key2, void *ctx __maybe_unused) > > +{ > > + const struct evsel *a = key1; > > + const struct evsel *b = key2; > > + > > + return a->core.attr.type == b->core.attr.type; > > +} > > + > > static void evsel__disable_missing_features(struct evsel *evsel) > > { > > if (perf_missing_features.weight_struct) { > > @@ -1807,8 +1828,14 @@ 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) > > - evsel->core.attr.exclude_guest = evsel->core.attr.exclude_host = 0; > > + if (perf_missing_features.exclude_guest) { > > + void *pmu; > > could you just pass NULL in here instead of NULL? > > > + > > + if (hashmap__find(perf_missing_features.pmu, evsel, &pmu)) { > > + evsel->core.attr.exclude_guest = 0; > > + evsel->core.attr.exclude_host = 0; > > + } > > + } > > if (perf_missing_features.lbr_flags) > > evsel->core.attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS | > > PERF_SAMPLE_BRANCH_NO_CYCLES); > > @@ -1840,6 +1867,9 @@ int evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus, > > > > bool evsel__detect_missing_features(struct evsel *evsel) > > { > > + if (perf_missing_features.pmu == NULL) > > + perf_missing_features.pmu = hashmap__new(pmu_hash, pmu_equal, NULL); > > + > > /* > > * Must probe features in the order they were added to the > > * perf_event_attr interface. > > @@ -1900,10 +1930,15 @@ 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) && > > + !hashmap__find(perf_missing_features.pmu, evsel, NULL)) { > > + struct perf_missing_pmu_features pmu_features = { true }; > > missing new line after declaration
ok
> > > + hashmap__add(perf_missing_features.pmu, evsel, &pmu_features); > > + > > + 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 1f7edfa8568a..8dd11c8e022d 100644 > > --- a/tools/perf/util/evsel.h > > +++ b/tools/perf/util/evsel.h > > @@ -172,6 +172,12 @@ struct perf_missing_features { > > bool data_page_size; > > bool code_page_size; > > bool weight_struct; > > + > > + struct hashmap *pmu; > > +}; > > + > > +struct perf_missing_pmu_features { > > + bool exclude_guest; > > }; > > hum, is this really needed? I think you could just pass '1' as value, > because you care only if the item is hashed, right?
It's not really needed, but I thought it might be useful to extend if we want to add another pmu-specific feature check later. But at this point I don't have a specific feature to add though.
> > in any case the value is the current stack address of the > struct perf_missing_pmu_features pmu_features = { true }; > > so it might as well be just '1' ... I was confused at the beggining > and looked for the reason of this struct ;-)
Right, as I said it's not need to be a struct and we can pass a scalar value instead if you want.
Thanks, Namhyung
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