Messages in this thread | | | Date | Sun, 28 Nov 2021 17:23:20 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH v2] perf metric: Reduce multiplexing with duration_time |
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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
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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