Re: [PATCH 3/4] perf parse-events: Don't move slots event when no topdwon metrics event

Liang, Kan
2024-07-02T18:03:43Z

On 2024-07-02 6:40 p.m., Dapeng Mi wrote:
> Currently the helper arch_evlist__cmp() would unconditionally move slots
> event to be the leader event even though there is no topdown metrics
> event in the group.
>
> perf stat -e "{instructions,slots}" -C 0 sleep 1
> WARNING: events were regrouped to match PMUs
>
> Performance counter stats for 'CPU(s) 0':
>
> 27,581,148 slots
> 8,390,827 instructions
>
> 1.045546595 seconds time elapsed
>
> This is an overkill. It's not necessary to move slots event as the leader
> event if there is no topdown metrics event.
>
> Thus only regroup events when there are both topdown slots and metrics
> events in a group.
>
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> ---
> tools/perf/arch/x86/util/evlist.c | 6 ++++--
> tools/perf/util/evlist.h | 7 ++++++-
> tools/perf/util/parse-events.c | 35 ++++++++++++++++++-------------
> 3 files changed, 31 insertions(+), 17 deletions(-)
>
> diff --git a/tools/perf/arch/x86/util/evlist.c b/tools/perf/arch/x86/util/evlist.c
> index 7215c7c7b435..a1e78be6ebd1 100644
> --- a/tools/perf/arch/x86/util/evlist.c
> +++ b/tools/perf/arch/x86/util/evlist.c
> @@ -73,9 +73,11 @@ int arch_evlist__add_default_attrs(struct evlist *evlist,
> return ___evlist__add_default_attrs(evlist, attrs, nr_attrs);
> }
>
> -int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs)
> +int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs, void *priv)
> {
> - if (topdown_sys_has_perf_metrics() &&
> + struct sort_priv *_priv = priv;
> +
> + if (topdown_sys_has_perf_metrics() && _priv->topdown_metrics_in_group &&
> (arch_evsel__must_be_in_group(lhs) || arch_evsel__must_be_in_group(rhs))) {
> /* Ensure the topdown slots comes first. */
> if (strcasestr(lhs->name, "slots") && !strcasestr(lhs->name, "uops_retired.slots"))
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index cb91dc9117a2..14c858dcf5a2 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -89,6 +89,11 @@ struct evsel_str_handler {
> void *handler;
> };
>
> +struct sort_priv {
> + int force_grouped_idx;
> + bool topdown_metrics_in_group;

The topdown metrics should be only available in some Intel platforms. I
don't think we want to add such platform-specific variable in the
generic code.

The current code just re-order the events, not re-group. So it doesn't
impact the result accuracy.
So the issue is just an annoying WARNING, right?

It seems the issue has been there for more than 1 year. No complaints
except for one internal test case, which can be easily fixed.
Considering the complexity of the fix, I guess we may leave it as is.

Thanks,
Kan
> +};
> +
> struct evlist *evlist__new(void);
> struct evlist *evlist__new_default(void);
> struct evlist *evlist__new_dummy(void);
> @@ -112,7 +117,7 @@ int arch_evlist__add_default_attrs(struct evlist *evlist,
> #define evlist__add_default_attrs(evlist, array) \
> arch_evlist__add_default_attrs(evlist, array, ARRAY_SIZE(array))
>
> -int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs);
> +int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs, void *priv);
>
> int evlist__add_dummy(struct evlist *evlist);
> struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide);
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 6ed0f9c5581d..a3f7173a7ae2 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -1962,19 +1962,21 @@ static int evsel__compute_group_pmu_name(struct evsel *evsel,
> return evsel->group_pmu_name ? 0 : -ENOMEM;
> }
>
> -__weak int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs)
> +__weak int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs,
> + void *priv __maybe_unused)
> {
> /* Order by insertion index. */
> return lhs->core.idx - rhs->core.idx;
> }
>
> -static int evlist__cmp(void *_fg_idx, const struct list_head *l, const struct list_head *r)
> +static int evlist__cmp(void *_sort_priv, const struct list_head *l, const struct list_head *r)
> {
> const struct perf_evsel *lhs_core = container_of(l, struct perf_evsel, node);
> const struct evsel *lhs = container_of(lhs_core, struct evsel, core);
> const struct perf_evsel *rhs_core = container_of(r, struct perf_evsel, node);
> const struct evsel *rhs = container_of(rhs_core, struct evsel, core);
> - int *force_grouped_idx = _fg_idx;
> + struct sort_priv *sort_priv = _sort_priv;
> + int force_grouped_idx = sort_priv->force_grouped_idx;
> int lhs_sort_idx, rhs_sort_idx, ret;
> const char *lhs_pmu_name, *rhs_pmu_name;
> bool lhs_has_group, rhs_has_group;
> @@ -1992,8 +1994,8 @@ static int evlist__cmp(void *_fg_idx, const struct list_head *l, const struct li
> lhs_sort_idx = lhs_core->leader->idx;
> } else {
> lhs_has_group = false;
> - lhs_sort_idx = *force_grouped_idx != -1 && arch_evsel__must_be_in_group(lhs)
> - ? *force_grouped_idx
> + lhs_sort_idx = force_grouped_idx != -1 && arch_evsel__must_be_in_group(lhs)
> + ? force_grouped_idx
> : lhs_core->idx;
> }
> if (rhs_core->leader != rhs_core || rhs_core->nr_members > 1) {
> @@ -2001,8 +2003,8 @@ static int evlist__cmp(void *_fg_idx, const struct list_head *l, const struct li
> rhs_sort_idx = rhs_core->leader->idx;
> } else {
> rhs_has_group = false;
> - rhs_sort_idx = *force_grouped_idx != -1 && arch_evsel__must_be_in_group(rhs)
> - ? *force_grouped_idx
> + rhs_sort_idx = force_grouped_idx != -1 && arch_evsel__must_be_in_group(rhs)
> + ? force_grouped_idx
> : rhs_core->idx;
> }
>
> @@ -2019,16 +2021,17 @@ static int evlist__cmp(void *_fg_idx, const struct list_head *l, const struct li
> }
>
> /* Architecture specific sorting. */
> - return arch_evlist__cmp(lhs, rhs);
> + return arch_evlist__cmp(lhs, rhs, _sort_priv);
> }
>
> static int parse_events__sort_events_and_fix_groups(struct list_head *list)
> {
> - int idx = 0, force_grouped_idx = -1;
> struct evsel *pos, *cur_leader = NULL;
> struct perf_evsel *cur_leaders_grp = NULL;
> bool idx_changed = false, cur_leader_force_grouped = false;
> int orig_num_leaders = 0, num_leaders = 0;
> + struct sort_priv sort_priv = {-1, false};
> + int idx = 0;
> int ret;
>
> /*
> @@ -2053,13 +2056,17 @@ static int parse_events__sort_events_and_fix_groups(struct list_head *list)
> pos->core.idx = idx++;
>
> /* Remember an index to sort all forced grouped events together to. */
> - if (force_grouped_idx == -1 && pos == pos_leader && pos->core.nr_members < 2 &&
> - arch_evsel__must_be_in_group(pos))
> - force_grouped_idx = pos->core.idx;
> + if (sort_priv.force_grouped_idx == -1 && pos == pos_leader &&
> + pos->core.nr_members < 2 && arch_evsel__must_be_in_group(pos))
> + sort_priv.force_grouped_idx = pos->core.idx;
> +
> + if (!sort_priv.topdown_metrics_in_group &&
> + strcasestr(pos->name, "topdown"))
> + sort_priv.topdown_metrics_in_group = true;
> }
>
> /* Sort events. */
> - list_sort(&force_grouped_idx, list, evlist__cmp);
> + list_sort(&sort_priv, list, evlist__cmp);
>
> /*
> * Recompute groups, splitting for PMUs and adding groups for events
> @@ -2070,7 +2077,7 @@ static int parse_events__sort_events_and_fix_groups(struct list_head *list)
> const struct evsel *pos_leader = evsel__leader(pos);
> const char *pos_pmu_name = pos->group_pmu_name;
> const char *cur_leader_pmu_name;
> - bool pos_force_grouped = force_grouped_idx != -1 &&
> + bool pos_force_grouped = sort_priv.force_grouped_idx != -1 &&
> arch_evsel__must_be_in_group(pos);
>
> /* Reset index and nr_members. */