Messages in this thread | | | From | Namhyung Kim <> | Date | Tue, 26 Oct 2021 12:30:42 -0700 | Subject | Re: [PATCH v2] perf evsel: Fix missing exclude_{host,guest} setting |
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Hi Jiri,
On Tue, Oct 26, 2021 at 11:32 AM Jiri Olsa <jolsa@redhat.com> wrote: > > On Mon, Oct 25, 2021 at 09:33:51PM -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> > > --- > > 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 | 47 +++++++++++++++++++++++++++++++++++------ > > tools/perf/util/evsel.h | 7 ++++++ > > 2 files changed, 48 insertions(+), 6 deletions(-) > > > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > > index dbfeceb2546c..f33801b4615d 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; > > should this just remove evsel from perf_missing_features.pmu?
Nop, it'll release all the hash nodes (pmu). Each evsel can come from a same PMU.
> > I'm not sure when we should actually release this.. what's your rationale > for releasing it in here?
Yeah, that's a problem when we should release it. Maybe we can add a function and call it in the exit path but I didn't want to change all the callsites just for this.
As evsel__delete() is called in the exit path, I thought it's a place where we can free the hashmap. But I'm not very happy with that either.. Do you have a better idea?
If another evsel is open after this function, I think it should be fine since it will create a new hash map and check the missing feature again.
> > > } > > > > 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 +1828,13 @@ 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) { > > + /* we only have EXCLUDE_GUEST bit, let's skip checking */ > > + if (hashmap__find(perf_missing_features.pmu, evsel, NULL)) { > > + 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 +1866,9 @@ 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); > > missing allocation fail check
Ok, will change.
Thanks for your review, Namhyung
> > > + > > /* > > * Must probe features in the order they were added to the > > * perf_event_attr interface. > > @@ -1900,10 +1929,16 @@ 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)) { > > + uintptr_t pmu_features = PERF_MISSING_PMU_EXCLUDE_GUEST; > > + > > + hashmap__add(perf_missing_features.pmu, evsel, (void *)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..11b5ece19f0e 100644 > > --- a/tools/perf/util/evsel.h > > +++ b/tools/perf/util/evsel.h > > @@ -172,6 +172,13 @@ struct perf_missing_features { > > bool data_page_size; > > bool code_page_size; > > bool weight_struct; > > + > > + /* contains enum perf_missing_pmu_features below */ > > + struct hashmap *pmu; > > +}; > > + > > +enum perf_missing_pmu_features { > > + PERF_MISSING_PMU_EXCLUDE_GUEST = 1UL << 0, > > }; > > > > extern struct perf_missing_features perf_missing_features; > > -- > > 2.33.0.1079.g6e70778dc9-goog > > >
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