Messages in this thread | | | Date | Tue, 30 Nov 2021 19:11:36 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH v2] perf metric: Reduce multiplexing with duration_time |
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On Mon, Nov 29, 2021 at 09:46:31AM -0800, Ian Rogers wrote: > On Sun, Nov 28, 2021 at 8:23 AM Jiri Olsa <jolsa@redhat.com> wrote: > > > > On Tue, Nov 23, 2021 at 05:52:26PM -0800, Ian Rogers wrote: > > > It is common to use the same counters with and without > > > duration_time. The ID sharing code treats duration_time as if it > > > were a hardware event placed in the same group. This causes > > > unnecessary multiplexing such as in the following example where > > > l3_cache_access isn't shared: > > > > > > $ perf stat -M l3 -a sleep 1 > > > > > > Performance counter stats for 'system wide': > > > > > > 3,117,007 l3_cache_miss # 199.5 MB/s l3_rd_bw > > > # 43.6 % l3_hits > > > # 56.4 % l3_miss (50.00%) > > > 5,526,447 l3_cache_access (50.00%) > > > 5,392,435 l3_cache_access # 5389191.2 access/s l3_access_rate (50.00%) > > > 1,000,601,901 ns duration_time > > > > > > 1.000601901 seconds time elapsed > > > > > > Fix this by placing duration_time in all groups unless metric > > > sharing has been disabled on the command line: > > > > > > $ perf stat -M l3 -a sleep 1 > > > > > > Performance counter stats for 'system wide': > > > > > > 3,597,972 l3_cache_miss # 230.3 MB/s l3_rd_bw > > > # 48.0 % l3_hits > > > # 52.0 % l3_miss > > > 6,914,459 l3_cache_access # 6909935.9 access/s l3_access_rate > > > 1,000,654,579 ns duration_time > > > > > > 1.000654579 seconds time elapsed > > > > > > $ perf stat --metric-no-merge -M l3 -a sleep 1 > > > > > > Performance counter stats for 'system wide': > > > > > > 3,501,834 l3_cache_miss # 53.5 % l3_miss (24.99%) > > > 6,548,173 l3_cache_access (24.99%) > > > 3,417,622 l3_cache_miss # 45.7 % l3_hits (25.04%) > > > 6,294,062 l3_cache_access (25.04%) > > > 5,923,238 l3_cache_access # 5919688.1 access/s l3_access_rate (24.99%) > > > 1,000,599,683 ns duration_time > > > 3,607,486 l3_cache_miss # 230.9 MB/s l3_rd_bw (49.97%) > > > > > > 1.000599683 seconds time elapsed > > > > > > v2. Doesn't count duration_time in the metric_list_cmp function that > > > sorts larger metrics first. Without this a metric with duration_time > > > and an event is sorted the same as a metric with two events, > > > possibly not allowing the first metric to share with the second. > > > > hum, isn't the change about adding duration_time in every metric? > > or you could still end up with metric without duration_time > > It is about adding duration_time to all metrics. Sorting of the > metrics by number of IDs happens before we insert duration_time which > happens just prior to parsing. duration_time needn't be inserted if > --metric-no-merge is passed.
I see, so that sorting takes place before it's added, makes sense then
Acked-by: Jiri Olsa <jolsa@redhat.com>
thanks, jirka
> > Thanks, > Ian > > > thanks, > > jirka > > > > > > > > Signed-off-by: Ian Rogers <irogers@google.com> > > > --- > > > tools/perf/util/metricgroup.c | 42 +++++++++++++++++++++++++++-------- > > > 1 file changed, 33 insertions(+), 9 deletions(-) > > > > > > diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c > > > index fffe02aae3ed..51c99cb08abf 100644 > > > --- a/tools/perf/util/metricgroup.c > > > +++ b/tools/perf/util/metricgroup.c > > > @@ -1115,13 +1115,27 @@ static int metricgroup__add_metric_sys_event_iter(const struct pmu_event *pe, > > > return ret; > > > } > > > > > > +/** > > > + * metric_list_cmp - list_sort comparator that sorts metrics with more events to > > > + * the front. duration_time is excluded from the count. > > > + */ > > > static int metric_list_cmp(void *priv __maybe_unused, const struct list_head *l, > > > const struct list_head *r) > > > { > > > const struct metric *left = container_of(l, struct metric, nd); > > > const struct metric *right = container_of(r, struct metric, nd); > > > + struct expr_id_data *data; > > > + int left_count, right_count; > > > + > > > + left_count = hashmap__size(left->pctx->ids); > > > + if (!expr__get_id(left->pctx, "duration_time", &data)) > > > + left_count--; > > > + > > > + right_count = hashmap__size(right->pctx->ids); > > > + if (!expr__get_id(right->pctx, "duration_time", &data)) > > > + right_count--; > > > > > > - return hashmap__size(right->pctx->ids) - hashmap__size(left->pctx->ids); > > > + return right_count - left_count; > > > } > > > > > > /** > > > @@ -1299,14 +1313,16 @@ static int build_combined_expr_ctx(const struct list_head *metric_list, > > > /** > > > * parse_ids - Build the event string for the ids and parse them creating an > > > * evlist. The encoded metric_ids are decoded. > > > + * @metric_no_merge: is metric sharing explicitly disabled. > > > * @fake_pmu: used when testing metrics not supported by the current CPU. > > > * @ids: the event identifiers parsed from a metric. > > > * @modifier: any modifiers added to the events. > > > * @has_constraint: false if events should be placed in a weak group. > > > * @out_evlist: the created list of events. > > > */ > > > -static int parse_ids(struct perf_pmu *fake_pmu, struct expr_parse_ctx *ids, > > > - const char *modifier, bool has_constraint, struct evlist **out_evlist) > > > +static int parse_ids(bool metric_no_merge, struct perf_pmu *fake_pmu, > > > + struct expr_parse_ctx *ids, const char *modifier, > > > + bool has_constraint, struct evlist **out_evlist) > > > { > > > struct parse_events_error parse_error; > > > struct evlist *parsed_evlist; > > > @@ -1314,12 +1330,19 @@ static int parse_ids(struct perf_pmu *fake_pmu, struct expr_parse_ctx *ids, > > > int ret; > > > > > > *out_evlist = NULL; > > > - if (hashmap__size(ids->ids) == 0) { > > > + if (!metric_no_merge || hashmap__size(ids->ids) == 0) { > > > char *tmp; > > > /* > > > - * No ids/events in the expression parsing context. Events may > > > - * have been removed because of constant evaluation, e.g.: > > > - * event1 if #smt_on else 0 > > > + * We may fail to share events between metrics because > > > + * duration_time isn't present in one metric. For example, a > > > + * ratio of cache misses doesn't need duration_time but the same > > > + * events may be used for a misses per second. Events without > > > + * sharing implies multiplexing, that is best avoided, so place > > > + * duration_time in every group. > > > + * > > > + * Also, there may be no ids/events in the expression parsing > > > + * context because of constant evaluation, e.g.: > > > + * event1 if #smt_on else 0 > > > * Add a duration_time event to avoid a parse error on an empty > > > * string. > > > */ > > > @@ -1387,7 +1410,8 @@ static int parse_groups(struct evlist *perf_evlist, const char *str, > > > ret = build_combined_expr_ctx(&metric_list, &combined); > > > > > > if (!ret && combined && hashmap__size(combined->ids)) { > > > - ret = parse_ids(fake_pmu, combined, /*modifier=*/NULL, > > > + ret = parse_ids(metric_no_merge, fake_pmu, combined, > > > + /*modifier=*/NULL, > > > /*has_constraint=*/true, > > > &combined_evlist); > > > } > > > @@ -1435,7 +1459,7 @@ static int parse_groups(struct evlist *perf_evlist, const char *str, > > > } > > > } > > > if (!metric_evlist) { > > > - ret = parse_ids(fake_pmu, m->pctx, m->modifier, > > > + ret = parse_ids(metric_no_merge, fake_pmu, m->pctx, m->modifier, > > > m->has_constraint, &m->evlist); > > > if (ret) > > > goto out; > > > -- > > > 2.34.0.rc2.393.gf8c9666880-goog > > > > > >
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