perf streams: Introduce branch history "streams"

We define a stream as the branch history which is aggregated by the
branch records from perf samples. For example, the callchains aggregated
from the branch records are considered as streams.  By browsing the hot
stream, we can understand the hot code path.

Now we only support the callchain for stream. For measuring the hot
level for a stream, we use the callchain_node->hit, higher is hotter.

There may be many callchains sampled so we only focus on the top N
hottest callchains. N is a user defined parameter or predefined default
value (nr_streams_max).

This patch creates an evsel_streams array per event, and saves the top N
hottest streams in a stream array.

So now we can get the per-event top N hottest streams.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20201009022845.13141-2-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/Build

@@ -102,6 +102,7 @@ perf-y += rwsem.o
 perf-y += thread-stack.o
 perf-y += spark.o
 perf-y += topdown.o
+perf-y += stream.o
 perf-$(CONFIG_AUXTRACE) += auxtrace.o
 perf-$(CONFIG_AUXTRACE) += intel-pt-decoder/
 perf-$(CONFIG_AUXTRACE) += intel-pt.o

tools/perf/util/stream.c

@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Compare and figure out the top N hottest streams
+ * Copyright (c) 2020, Intel Corporation.
+ * Author: Jin Yao
+ */
+
+#include <inttypes.h>
+#include <stdlib.h>
+#include <linux/zalloc.h>
+#include "debug.h"
+#include "hist.h"
+#include "sort.h"
+#include "stream.h"
+#include "evlist.h"
+
+static void evsel_streams__delete(struct evsel_streams *es, int nr_evsel)
+{
+	for (int i = 0; i < nr_evsel; i++)
+		zfree(&es[i].streams);
+
+	free(es);
+}
+
+void evlist_streams__delete(struct evlist_streams *els)
+{
+	evsel_streams__delete(els->ev_streams, els->nr_evsel);
+	free(els);
+}
+
+static struct evlist_streams *evlist_streams__new(int nr_evsel,
+						  int nr_streams_max)
+{
+	struct evlist_streams *els;
+	struct evsel_streams *es;
+
+	els = zalloc(sizeof(*els));
+	if (!els)
+		return NULL;
+
+	es = calloc(nr_evsel, sizeof(struct evsel_streams));
+	if (!es) {
+		free(els);
+		return NULL;
+	}
+
+	for (int i = 0; i < nr_evsel; i++) {
+		struct evsel_streams *s = &es[i];
+
+		s->streams = calloc(nr_streams_max, sizeof(struct stream));
+		if (!s->streams)
+			goto err;
+
+		s->nr_streams_max = nr_streams_max;
+		s->evsel_idx = -1;
+	}
+
+	els->ev_streams = es;
+	els->nr_evsel = nr_evsel;
+	return els;
+
+err:
+	evsel_streams__delete(es, nr_evsel);
+	return NULL;
+}
+
+/*
+ * The cnodes with high hit number are hot callchains.
+ */
+static void evsel_streams__set_hot_cnode(struct evsel_streams *es,
+					 struct callchain_node *cnode)
+{
+	int i, idx = 0;
+	u64 hit;
+
+	if (es->nr_streams < es->nr_streams_max) {
+		i = es->nr_streams;
+		es->streams[i].cnode = cnode;
+		es->nr_streams++;
+		return;
+	}
+
+	/*
+	 * Considering a few number of hot streams, only use simple
+	 * way to find the cnode with smallest hit number and replace.
+	 */
+	hit = (es->streams[0].cnode)->hit;
+	for (i = 1; i < es->nr_streams; i++) {
+		if ((es->streams[i].cnode)->hit < hit) {
+			hit = (es->streams[i].cnode)->hit;
+			idx = i;
+		}
+	}
+
+	if (cnode->hit > hit)
+		es->streams[idx].cnode = cnode;
+}
+
+static void update_hot_callchain(struct hist_entry *he,
+				 struct evsel_streams *es)
+{
+	struct rb_root *root = &he->sorted_chain;
+	struct rb_node *rb_node = rb_first(root);
+	struct callchain_node *cnode;
+
+	while (rb_node) {
+		cnode = rb_entry(rb_node, struct callchain_node, rb_node);
+		evsel_streams__set_hot_cnode(es, cnode);
+		rb_node = rb_next(rb_node);
+	}
+}
+
+static void init_hot_callchain(struct hists *hists, struct evsel_streams *es)
+{
+	struct rb_node *next = rb_first_cached(&hists->entries);
+
+	while (next) {
+		struct hist_entry *he;
+
+		he = rb_entry(next, struct hist_entry, rb_node);
+		update_hot_callchain(he, es);
+		next = rb_next(&he->rb_node);
+	}
+}
+
+static int evlist__init_callchain_streams(struct evlist *evlist,
+					  struct evlist_streams *els)
+{
+	struct evsel_streams *es = els->ev_streams;
+	struct evsel *pos;
+	int i = 0;
+
+	BUG_ON(els->nr_evsel < evlist->core.nr_entries);
+
+	evlist__for_each_entry(evlist, pos) {
+		struct hists *hists = evsel__hists(pos);
+
+		hists__output_resort(hists, NULL);
+		init_hot_callchain(hists, &es[i]);
+		es[i].evsel_idx = pos->idx;
+		i++;
+	}
+
+	return 0;
+}
+
+struct evlist_streams *evlist__create_streams(struct evlist *evlist,
+					      int nr_streams_max)
+{
+	int nr_evsel = evlist->core.nr_entries, ret = -1;
+	struct evlist_streams *els = evlist_streams__new(nr_evsel,
+							 nr_streams_max);
+
+	if (!els)
+		return NULL;
+
+	ret = evlist__init_callchain_streams(evlist, els);
+	if (ret) {
+		evlist_streams__delete(els);
+		return NULL;
+	}
+
+	return els;
+}

tools/perf/util/stream.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_STREAM_H
+#define __PERF_STREAM_H
+
+#include "callchain.h"
+
+struct stream {
+	struct callchain_node	*cnode;
+};
+
+struct evsel_streams {
+	struct stream		*streams;
+	int			nr_streams_max;
+	int			nr_streams;
+	int			evsel_idx;
+};
+
+struct evlist_streams {
+	struct evsel_streams	*ev_streams;
+	int			nr_evsel;
+};
+
+struct evlist;
+
+void evlist_streams__delete(struct evlist_streams *els);
+
+struct evlist_streams *evlist__create_streams(struct evlist *evlist,
+					      int nr_streams_max);
+
+#endif /* __PERF_STREAM_H */