[PATCH v3 0/2] perf hist: Fix bogus profiles when filters are enabled

[PATCH v3 0/2] perf hist: Fix bogus profiles when filters are enabled

[Dmitry Vyukov]

Dmitry Vyukov (2):
  perf hist: Deduplicate cmp/sort/collapse code
  perf hist: Fix bogus profiles when filters are enabled

 tools/perf/util/hist.c | 114 +++++++++++++++++++----------------------
 tools/perf/util/hist.h |  14 +++--
 2 files changed, 59 insertions(+), 69 deletions(-)


base-commit: 619f0b6fad524f08d493a98d55bac9ab8895e3a6
-- 
2.48.0.rc2.279.g1de40edade-goog

[PATCH v3 1/2] perf hist: Deduplicate cmp/sort/collapse code

[Dmitry Vyukov]

Application of cmp/sort/collapse fmt callbacks is duplicated 6 times.
Factor it into a common helper function. NFC.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

---

Changes in v2:
 - add perf_hpp_fmt_cmp_t typedef to util/hist.h
 - use the typedef for perf_hpp_fmt::{cmp,collapse,sort}

Changes in v3:
 - make fn a pointer in hist_entry__cmp_impl()
---
 tools/perf/util/hist.c | 103 +++++++++++++++++------------------------
 tools/perf/util/hist.h |  14 +++---
 2 files changed, 49 insertions(+), 68 deletions(-)

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index fff1345658016..493b3cc30eac0 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -32,6 +32,9 @@
 #include <linux/time64.h>
 #include <linux/zalloc.h>
 
+static int64_t hist_entry__cmp(struct hist_entry *left, struct hist_entry *right);
+static int64_t hist_entry__collapse(struct hist_entry *left, struct hist_entry *right);
+
 static bool hists__filter_entry_by_dso(struct hists *hists,
 				       struct hist_entry *he);
 static bool hists__filter_entry_by_thread(struct hists *hists,
@@ -1292,19 +1295,26 @@ int hist_entry_iter__add(struct hist_entry_iter *iter, struct addr_location *al,
 	return err;
 }
 
-int64_t
-hist_entry__cmp(struct hist_entry *left, struct hist_entry *right)
+static int64_t
+hist_entry__cmp_impl(struct perf_hpp_list *hpp_list, struct hist_entry *left,
+		     struct hist_entry *right, unsigned long fn_offset,
+		     bool ignore_dynamic, bool ignore_skipped)
 {
 	struct hists *hists = left->hists;
 	struct perf_hpp_fmt *fmt;
+	perf_hpp_fmt_cmp_t *fn;
 	int64_t cmp = 0;
 
-	hists__for_each_sort_list(hists, fmt) {
-		if (perf_hpp__is_dynamic_entry(fmt) &&
+	perf_hpp_list__for_each_sort_list(hpp_list, fmt) {
+		if (ignore_dynamic && perf_hpp__is_dynamic_entry(fmt) &&
 		    !perf_hpp__defined_dynamic_entry(fmt, hists))
 			continue;
 
-		cmp = fmt->cmp(fmt, left, right);
+		if (ignore_skipped && perf_hpp__should_skip(fmt, hists))
+			continue;
+
+		fn = (void *)fmt + fn_offset;
+		cmp = (*fn)(fmt, left, right);
 		if (cmp)
 			break;
 	}
@@ -1313,23 +1323,33 @@ hist_entry__cmp(struct hist_entry *left, struct hist_entry *right)
 }
 
 int64_t
-hist_entry__collapse(struct hist_entry *left, struct hist_entry *right)
+hist_entry__cmp(struct hist_entry *left, struct hist_entry *right)
 {
-	struct hists *hists = left->hists;
-	struct perf_hpp_fmt *fmt;
-	int64_t cmp = 0;
+	return hist_entry__cmp_impl(left->hists->hpp_list, left, right,
+		offsetof(struct perf_hpp_fmt, cmp), true, false);
+}
 
-	hists__for_each_sort_list(hists, fmt) {
-		if (perf_hpp__is_dynamic_entry(fmt) &&
-		    !perf_hpp__defined_dynamic_entry(fmt, hists))
-			continue;
+static int64_t
+hist_entry__sort(struct hist_entry *left, struct hist_entry *right)
+{
+	return hist_entry__cmp_impl(left->hists->hpp_list, left, right,
+		offsetof(struct perf_hpp_fmt, sort), false, true);
+}
 
-		cmp = fmt->collapse(fmt, left, right);
-		if (cmp)
-			break;
-	}
+int64_t
+hist_entry__collapse(struct hist_entry *left, struct hist_entry *right)
+{
+	return hist_entry__cmp_impl(left->hists->hpp_list, left, right,
+		offsetof(struct perf_hpp_fmt, collapse), true, false);
+}
 
-	return cmp;
+static int64_t
+hist_entry__collapse_hierarchy(struct perf_hpp_list *hpp_list,
+			       struct hist_entry *left,
+			       struct hist_entry *right)
+{
+	return hist_entry__cmp_impl(hpp_list, left, right,
+		offsetof(struct perf_hpp_fmt, collapse), false, false);
 }
 
 void hist_entry__delete(struct hist_entry *he)
@@ -1503,14 +1523,7 @@ static struct hist_entry *hierarchy_insert_entry(struct hists *hists,
 	while (*p != NULL) {
 		parent = *p;
 		iter = rb_entry(parent, struct hist_entry, rb_node_in);
-
-		cmp = 0;
-		perf_hpp_list__for_each_sort_list(hpp_list, fmt) {
-			cmp = fmt->collapse(fmt, iter, he);
-			if (cmp)
-				break;
-		}
-
+		cmp = hist_entry__collapse_hierarchy(hpp_list, iter, he);
 		if (!cmp) {
 			he_stat__add_stat(&iter->stat, &he->stat);
 			return iter;
@@ -1730,24 +1743,6 @@ int hists__collapse_resort(struct hists *hists, struct ui_progress *prog)
 	return 0;
 }
 
-static int64_t hist_entry__sort(struct hist_entry *a, struct hist_entry *b)
-{
-	struct hists *hists = a->hists;
-	struct perf_hpp_fmt *fmt;
-	int64_t cmp = 0;
-
-	hists__for_each_sort_list(hists, fmt) {
-		if (perf_hpp__should_skip(fmt, a->hists))
-			continue;
-
-		cmp = fmt->sort(fmt, a, b);
-		if (cmp)
-			break;
-	}
-
-	return cmp;
-}
-
 static void hists__reset_filter_stats(struct hists *hists)
 {
 	hists->nr_non_filtered_entries = 0;
@@ -2449,21 +2444,15 @@ static struct hist_entry *add_dummy_hierarchy_entry(struct hists *hists,
 	struct rb_node **p;
 	struct rb_node *parent = NULL;
 	struct hist_entry *he;
-	struct perf_hpp_fmt *fmt;
 	bool leftmost = true;
 
 	p = &root->rb_root.rb_node;
 	while (*p != NULL) {
-		int64_t cmp = 0;
+		int64_t cmp;
 
 		parent = *p;
 		he = rb_entry(parent, struct hist_entry, rb_node_in);
-
-		perf_hpp_list__for_each_sort_list(he->hpp_list, fmt) {
-			cmp = fmt->collapse(fmt, he, pair);
-			if (cmp)
-				break;
-		}
+		cmp = hist_entry__collapse_hierarchy(he->hpp_list, he, pair);
 		if (!cmp)
 			goto out;
 
@@ -2521,16 +2510,10 @@ static struct hist_entry *hists__find_hierarchy_entry(struct rb_root_cached *roo
 
 	while (n) {
 		struct hist_entry *iter;
-		struct perf_hpp_fmt *fmt;
-		int64_t cmp = 0;
+		int64_t cmp;
 
 		iter = rb_entry(n, struct hist_entry, rb_node_in);
-		perf_hpp_list__for_each_sort_list(he->hpp_list, fmt) {
-			cmp = fmt->collapse(fmt, iter, he);
-			if (cmp)
-				break;
-		}
-
+		cmp = hist_entry__collapse_hierarchy(he->hpp_list, iter, he);
 		if (cmp < 0)
 			n = n->rb_left;
 		else if (cmp > 0)
diff --git a/tools/perf/util/hist.h b/tools/perf/util/hist.h
index 1131056924d9c..46c8373e31465 100644
--- a/tools/perf/util/hist.h
+++ b/tools/perf/util/hist.h
@@ -342,8 +342,6 @@ int hist_entry_iter__add(struct hist_entry_iter *iter, struct addr_location *al,
 struct perf_hpp;
 struct perf_hpp_fmt;
 
-int64_t hist_entry__cmp(struct hist_entry *left, struct hist_entry *right);
-int64_t hist_entry__collapse(struct hist_entry *left, struct hist_entry *right);
 int hist_entry__transaction_len(void);
 int hist_entry__sort_snprintf(struct hist_entry *he, char *bf, size_t size,
 			      struct hists *hists);
@@ -452,6 +450,9 @@ struct perf_hpp {
 	bool skip;
 };
 
+typedef int64_t (*perf_hpp_fmt_cmp_t)(
+	struct perf_hpp_fmt *, struct hist_entry *, struct hist_entry *);
+
 struct perf_hpp_fmt {
 	const char *name;
 	int (*header)(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
@@ -463,12 +464,9 @@ struct perf_hpp_fmt {
 		     struct hist_entry *he);
 	int (*entry)(struct perf_hpp_fmt *fmt, struct perf_hpp *hpp,
 		     struct hist_entry *he);
-	int64_t (*cmp)(struct perf_hpp_fmt *fmt,
-		       struct hist_entry *a, struct hist_entry *b);
-	int64_t (*collapse)(struct perf_hpp_fmt *fmt,
-			    struct hist_entry *a, struct hist_entry *b);
-	int64_t (*sort)(struct perf_hpp_fmt *fmt,
-			struct hist_entry *a, struct hist_entry *b);
+	perf_hpp_fmt_cmp_t cmp;
+	perf_hpp_fmt_cmp_t collapse;
+	perf_hpp_fmt_cmp_t sort;
 	bool (*equal)(struct perf_hpp_fmt *a, struct perf_hpp_fmt *b);
 	void (*free)(struct perf_hpp_fmt *fmt);
 
-- 
2.48.0.rc2.279.g1de40edade-goog

[PATCH v3 2/2] perf hist: Fix bogus profiles when filters are enabled

[Dmitry Vyukov]

When a filtered column is not present in the sort order, profiles become
arbitrary broken. Filtered and non-filtered entries are collapsed
together, and the filtered-by field ends up with a random value (either
from a filtered or non-filtered entry). If we end up with filtered
entry/value, then the whole collapsed entry will be filtered out and will
be missing in the profile. If we end up with non-filtered entry/value,
then the overhead value will be wrongly larger (include some subset
of filtered out samples).

This leads to very confusing profiles. The problem is hard to notice,
and if noticed hard to understand. If the filter is for a single value,
then it can be fixed by adding the corresponding field to the sort order
(provided user understood the problem). But if the filter is for multiple
values, it's impossible to fix b/c there is no concept of binary sorting
based on filter predicate (we want to group all non-filtered values in
one bucket, and all filtered values in another).

Examples of affected commands:
perf report --tid=123
perf report --sort overhead,symbol --comm=foo,bar

Fix this by considering filtered status as the highest priority
sort/collapse predicate.

As a side effect this effectively adds a new feature of showing profile
where several lines are combined based on arbitrary filtering predicate.
For example, showing symbols from binaries foo and bar combined together,
but not from other binaries; or showing combined overhead of several
particular threads.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 tools/perf/util/hist.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 493b3cc30eac0..0f30f843c566d 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -1303,7 +1303,16 @@ hist_entry__cmp_impl(struct perf_hpp_list *hpp_list, struct hist_entry *left,
 	struct hists *hists = left->hists;
 	struct perf_hpp_fmt *fmt;
 	perf_hpp_fmt_cmp_t *fn;
-	int64_t cmp = 0;
+	int64_t cmp;
+
+	/*
+	 * Never collapse filtered and non-filtered entries.
+	 * Note this is not the same as having an extra (invisible) fmt
+	 * that corresponds to the filtered status.
+	 */
+	cmp = (int64_t)!!left->filtered - (int64_t)!!right->filtered;
+	if (cmp)
+		return cmp;
 
 	perf_hpp_list__for_each_sort_list(hpp_list, fmt) {
 		if (ignore_dynamic && perf_hpp__is_dynamic_entry(fmt) &&
-- 
2.48.0.rc2.279.g1de40edade-goog

Re: [PATCH v3 0/2] perf hist: Fix bogus profiles when filters are enabled

[Namhyung Kim]

On Wed, 15 Jan 2025 09:00:40 +0100, Dmitry Vyukov wrote:

> Dmitry Vyukov (2):
>   perf hist: Deduplicate cmp/sort/collapse code
>   perf hist: Fix bogus profiles when filters are enabled
> 
>  tools/perf/util/hist.c | 114 +++++++++++++++++++----------------------
>  tools/perf/util/hist.h |  14 +++--
>  2 files changed, 59 insertions(+), 69 deletions(-)
> 
> [...]

Applied to perf-tools-next, thanks!

Best regards,
Namhyung