perf c2c: add function view stats merge and memory management

Add the per-entry stats/cstats aggregation helpers and hierarchy teardown.
Child common fields are released through hist_entry__delete(), while the
function-view free callback handles the private child tree and containing
allocation. Also add a helper for pruning writer entries with no stores or
cacheline children.

These are used by the entry-creation and builder patches that follow and
are __maybe_unused until then.

Signed-off-by: Jiebin Sun <jiebin.sun@intel.com>
Reviewed-by: Tianyou Li <tianyou.li@intel.com>
Reviewed-by: Wangyang Guo <wangyang.guo@intel.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/c2c-function.c

@@ -680,3 +680,166 @@ c2c_function_hists__reinit(struct c2c_hists *c2c_hists,
 
 	return function_hpp_list__parse(&c2c_hists->list, output, sort, env);
 }
+
+/* Welford online merge of two "stats" (from util/stat.h) accumulators. */
+static void c2c_stats_merge(struct stats *dest, const struct stats *src)
+{
+	double delta;
+
+	if (src->n == 0)
+		return;
+
+	if (dest->n == 0) {
+		*dest = *src;
+		return;
+	}
+
+	delta = src->mean - dest->mean;
+	dest->M2 += src->M2 + delta * delta * dest->n * src->n / (dest->n + src->n);
+	dest->mean = (dest->mean * dest->n + src->mean * src->n) / (dest->n + src->n);
+	dest->n += src->n;
+
+	/* Update min/max */
+	if (src->max > dest->max)
+		dest->max = src->max;
+	if (src->min < dest->min)
+		dest->min = src->min;
+}
+
+/* Merge compute_stats during function aggregation. */
+static void __maybe_unused c2c_add_cstats(struct compute_stats *dest,
+					  const struct compute_stats *src)
+{
+	c2c_stats_merge(&dest->rmt_hitm, &src->rmt_hitm);
+	c2c_stats_merge(&dest->lcl_hitm, &src->lcl_hitm);
+	c2c_stats_merge(&dest->rmt_peer, &src->rmt_peer);
+	c2c_stats_merge(&dest->lcl_peer, &src->lcl_peer);
+	c2c_stats_merge(&dest->load, &src->load);
+}
+
+static bool __maybe_unused hist_entry__add_c2c_stats(struct hist_entry *he,
+						     const struct c2c_stats *stats)
+{
+	u64 nr_events = c2c_hitm_count(stats) + stats->rmt_peer + stats->lcl_peer;
+	u64 weight1 = c2c_hitm_count(stats);
+
+	/*
+	 * Allocate before touching he->stat, so a failure here leaves the
+	 * entry unmodified and the caller can bail out without having
+	 * half-updated the statistics.
+	 */
+	if (symbol_conf.cumulate_callchain && !he->stat_acc) {
+		he->stat_acc = calloc(1, sizeof(struct he_stat));
+		if (!he->stat_acc)
+			return false;
+	}
+
+	he->stat.nr_events += nr_events;
+	he->stat.period += nr_events;
+	he->stat.weight1 += weight1;
+
+	if (!symbol_conf.cumulate_callchain)
+		return true;
+
+	he->stat_acc->nr_events += nr_events;
+	he->stat_acc->period += nr_events;
+	he->stat_acc->weight1 += weight1;
+
+	return true;
+}
+
+static void c2c_he__free_hierarchy(struct hist_entry *he);
+
+/*
+ * Free a function-view histogram entry (hist_entry_ops::free).
+ */
+static void __maybe_unused c2c_function_he_free(void *ptr)
+{
+	struct hist_entry *he = ptr;
+	struct c2c_hist_entry *c2c_he;
+
+	c2c_he = container_of(he, struct c2c_hist_entry, he);
+
+	if (c2c_he->hists) {
+		perf_hpp__reset_output_field(&c2c_he->hists->list);
+		hists__delete_all_entries(&c2c_he->hists->hists);
+		zfree(&c2c_he->hists);
+	}
+
+	c2c_he__free_hierarchy(he);
+
+	zfree(&c2c_he->nodeset);
+	zfree(&c2c_he->cpuset);
+	zfree(&c2c_he->nodestr);
+	zfree(&c2c_he->node_stats);
+
+	free(c2c_he);
+}
+
+static void c2c_he__free_hierarchy(struct hist_entry *he)
+{
+	struct rb_node *nd;
+	struct hist_entry *child_he;
+
+	/*
+	 * A leaf entry stores its callchains in the sorted_chain member, which
+	 * shares a union with the hroot_in/hroot_out child trees, so its
+	 * hroot_out is not a valid subtree to walk. Leaf entries never have a
+	 * child hierarchy here, so stop before touching hroot_out.
+	 */
+	if (he->leaf)
+		return;
+
+	if (RB_EMPTY_ROOT(&he->hroot_out.rb_root))
+		return;
+
+	nd = rb_first_cached(&he->hroot_out);
+	while (nd) {
+		struct rb_node *next = rb_next(nd);
+
+		child_he = rb_entry(nd, struct hist_entry, rb_node);
+		rb_erase_cached(&child_he->rb_node, &he->hroot_out);
+		hist_entry__delete(child_he);
+
+		nd = next;
+	}
+
+	/* All children erased; clear the tree (and its cached leftmost). */
+	he->hroot_out = RB_ROOT_CACHED;
+}
+
+/*
+ * Drop level-2 writing functions that carry no stores or
+ * no cacheline children. Writers are only added when they store into a shared
+ * line, so this is mainly a safety net. Returns the number of surviving
+ * writers.
+ */
+static int __maybe_unused c2c_he__prune_empty_writers(struct hist_entry *l1_he)
+{
+	struct rb_node *nd;
+	int surviving = 0;
+
+	if (!l1_he->has_children)
+		return 0;
+
+	nd = rb_first_cached(&l1_he->hroot_out);
+	while (nd) {
+		struct rb_node *next = rb_next(nd);
+		struct hist_entry *l2_he = rb_entry(nd, struct hist_entry, rb_node);
+
+		if (l2_he->has_children && hist_entry__displayed_stores(l2_he) > 0) {
+			surviving++;
+		} else {
+			rb_erase_cached(&l2_he->rb_node, &l1_he->hroot_out);
+			hist_entry__delete(l2_he);
+		}
+		nd = next;
+	}
+
+	if (!surviving) {
+		l1_he->hroot_out = RB_ROOT_CACHED;
+		l1_he->has_children = false;
+		l1_he->unfolded = false;
+	}
+	return surviving;
+}