[PATCH v1 2/7] perf ui hist: Add support for aggregated total_period and merging entries cleanly

[Ian Rogers <irogers@google.com>]

Implement cross-PMU histogram sorting logic and properly scale the
global total_period for symmetric percentage ceilings across differing
core types, resolving issues with --percent-limit.

Signed-off-by: Ian Rogers <irogers@google.com>
Assisted-by: Antigravity:gemini-3.1-pro
---
 tools/perf/ui/hist.c   | 49 ++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/hist.h |  5 +++++
 2 files changed, 54 insertions(+)

diff --git a/tools/perf/ui/hist.c b/tools/perf/ui/hist.c
index e58327595d37..09f0baa808e0 100644
--- a/tools/perf/ui/hist.c
+++ b/tools/perf/ui/hist.c
@@ -287,6 +287,24 @@ static int __hpp__sort(struct hist_entry *a, struct hist_entry *b,
 		return __hpp__group_sort_idx(a, b, get_field,
 					     symbol_conf.group_sort_idx);
 	}
+	/*
+	 * Relies on merge_entries being only enabled if there are
+	 * only matching events. If that is ever relaxed will need
+	 * more logic here.
+	 */
+	if (a->hists->merge_entries && b->hists->merge_entries) {
+		u64 val_a = get_field(a), val_b = get_field(b);
+		struct hist_entry *pair;
+
+		list_for_each_entry(pair, &a->pairs.head, pairs.node)
+			val_a += get_field(pair);
+		list_for_each_entry(pair, &b->pairs.head, pairs.node)
+			val_b += get_field(pair);
+
+		ret = field_cmp(val_a, val_b);
+		if (ret)
+			return ret;
+	}
 
 	ret = field_cmp(get_field(a), get_field(b));
 	if (ret || !symbol_conf.event_group)
@@ -1271,3 +1289,34 @@ int perf_hpp__alloc_mem_stats(struct perf_hpp_list *list, struct evlist *evlist)
 	}
 	return 0;
 }
+
+float hist_entry__get_percent_limit_merged(struct hist_entry *he)
+{
+	struct hist_entry *pair;
+	u64 period = he->stat.period;
+	u64 total_period = hists__total_period(he->hists);
+	struct evsel *evsel = hists_to_evsel(he->hists);
+	struct evsel *pos;
+
+	/* Accumulate global total_period across all merged hists */
+	for_each_group_member(pos, evsel) {
+		total_period += hists__total_period(evsel__hists(pos));
+	}
+
+	/* Accumulate symbol specific period across pairs */
+	list_for_each_entry(pair, &he->pairs.head, pairs.node) {
+		period += pair->stat.period;
+	}
+
+	if (unlikely(total_period == 0))
+		return 0;
+
+	if (symbol_conf.cumulate_callchain) {
+		period = he->stat_acc->period;
+		list_for_each_entry(pair, &he->pairs.head, pairs.node) {
+			period += pair->stat_acc->period;
+		}
+	}
+
+	return period * 100.0 / total_period;
+}
diff --git a/tools/perf/util/hist.h b/tools/perf/util/hist.h
index ea79628bbc6b..6cb7059e8405 100644
--- a/tools/perf/util/hist.h
+++ b/tools/perf/util/hist.h
@@ -434,6 +434,8 @@ void hists__match(struct hists *leader, struct hists *other);
 int hists__link(struct hists *leader, struct hists *other);
 int hists__unlink(struct hists *hists);
 
+float hist_entry__get_percent_limit_merged(struct hist_entry *he);
+
 static inline float hist_entry__get_percent_limit(struct hist_entry *he)
 {
 	u64 period = he->stat.period;
@@ -445,6 +447,9 @@ static inline float hist_entry__get_percent_limit(struct hist_entry *he)
 	if (symbol_conf.cumulate_callchain)
 		period = he->stat_acc->period;
 
+	if (he->hists->merge_entries)
+		return hist_entry__get_percent_limit_merged(he);
+
 	return period * 100.0 / total_period;
 }
 
-- 
2.55.0.766.g2966f0265a-goog