[PATCH v3 10/17] perf dsos: Use read lock fast path in dsos__findnew_id()

[Ian Rogers]

In dsos__findnew_id(), try finding the DSO under the read lock first and
only acquire the write lock when a new DSO must be inserted or an
existing DSO needs its ID updated (checked via dso__needs_improve_id()).

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/dso.c  | 16 +++++++++++++++-
 tools/perf/util/dso.h  |  1 +
 tools/perf/util/dsos.c | 10 ++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index f0e02062c09c..4dc518f7cb7d 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1685,6 +1685,18 @@ const struct dso_id dso_id_empty = {
 	}
 };
 
+bool dso__needs_improve_id(const struct dso *dso, const struct dso_id *id)
+{
+	const struct dso_id *dso_id = dso__id_const(dso);
+
+	if (!id)
+		return false;
+
+	return (id->mmap2_valid && !dso_id->mmap2_valid) ||
+	       (id->mmap2_ino_generation_valid && !dso_id->mmap2_ino_generation_valid) ||
+	       (build_id__is_defined(&id->build_id) && !build_id__is_defined(&dso_id->build_id));
+}
+
 void __dso__improve_id(struct dso *dso, const struct dso_id *id)
 {
 	struct dsos *dsos = dso__dsos(dso);
@@ -1692,6 +1704,8 @@ void __dso__improve_id(struct dso *dso, const struct dso_id *id)
 	bool changed = false;
 
 	/* dsos write lock held by caller. */
+	if (!id)
+		return;
 
 	if (id->mmap2_valid && !dso_id->mmap2_valid) {
 		dso_id->maj = id->maj;
@@ -1715,7 +1729,7 @@ void __dso__improve_id(struct dso *dso, const struct dso_id *id)
 
 int dso_id__cmp(const struct dso_id *a, const struct dso_id *b)
 {
-	if (a == &dso_id_empty || b == &dso_id_empty) {
+	if (!a || !b || a == &dso_id_empty || b == &dso_id_empty) {
 		/* There is no valid data to compare so the comparison always returns identical. */
 		return 0;
 	}
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 9f026ccb0eb6..394960cd2004 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -802,6 +802,7 @@ void dso__delete(struct dso *dso);
 int dso__cmp_id(struct dso *a, struct dso *b);
 void dso__set_short_name(struct dso *dso, const char *name, bool name_allocated);
 void dso__set_long_name(struct dso *dso, const char *name, bool name_allocated);
+bool dso__needs_improve_id(const struct dso *dso, const struct dso_id *id);
 void __dso__improve_id(struct dso *dso, const struct dso_id *id);
 
 int dso__name_len(const struct dso *dso);
diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
index 40267d3a725d..b5c8086941d5 100644
--- a/tools/perf/util/dsos.c
+++ b/tools/perf/util/dsos.c
@@ -348,6 +348,16 @@ static struct dso *__dsos__findnew_id(struct dsos *dsos, const char *name, const
 struct dso *dsos__findnew_id(struct dsos *dsos, const char *name, const struct dso_id *id)
 {
 	struct dso *dso;
+
+	down_read(&dsos->lock);
+	dso = __dsos__find_id(dsos, name, id, false, /*write_locked=*/false);
+	if (dso && !dso__needs_improve_id(dso, id)) {
+		up_read(&dsos->lock);
+		return dso;
+	}
+	up_read(&dsos->lock);
+	dso__put(dso);
+
 	down_write(&dsos->lock);
 	dso = __dsos__findnew_id(dsos, name, id);
 	up_write(&dsos->lock);
-- 
2.56.0.212.g129ede20d9-goog