linux-kernel - [PATCH 3/3] perf lock: Print lost entries at the end

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Message-Id: <20220802073511.299459-3-namhyung@kernel.org>
Date:   Tue,  2 Aug 2022 00:35:11 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Song Liu <songliubraving@...com>,
        Blake Jones <blakejones@...gle.com>
Subject: [PATCH 3/3] perf lock: Print lost entries at the end

Like the normal perf lock report output, it'd print bad stats at the end
if exists or -v option is passed.  Currently it uses BROKEN_CONTENDED
stat for the lost count (due to full stack maps).

  $ sudo perf lock con -a -b -m 128 sleep 5
  ...
  === output for debug===

  bad: 43, total: 14903
  bad rate: 0.29 %
  histogram of events caused bad sequence
      acquire: 0
     acquired: 0
    contended: 43
      release: 0

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/builtin-lock.c                      | 8 +++++++-
 tools/perf/util/bpf_lock_contention.c          | 6 ++++--
 tools/perf/util/bpf_skel/lock_contention.bpf.c | 9 +++++++--
 tools/perf/util/lock-contention.h              | 1 +
 4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index e32fdcd497e0..8065f0268e55 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -1471,8 +1471,11 @@ static void print_contention_result(void)
 		pr_info("  %10s   %s\n\n", "type", "caller");
 
 	bad = total = 0;
+	if (use_bpf)
+		bad = bad_hist[BROKEN_CONTENDED];
+
 	while ((st = pop_from_result())) {
-		total++;
+		total += use_bpf ? st->nr_contended : 1;
 		if (st->broken)
 			bad++;
 
@@ -1686,6 +1689,9 @@ static int __cmd_contention(int argc, const char **argv)
 
 		lock_contention_stop();
 		lock_contention_read(&con);
+
+		/* abuse bad hist stats for lost entries */
+		bad_hist[BROKEN_CONTENDED] = con.lost;
 	} else {
 		err = perf_session__process_events(session);
 		if (err)
diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index 26128e5bb659..65f51cc25236 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -16,7 +16,7 @@ static struct lock_contention_bpf *skel;
 
 /* should be same as bpf_skel/lock_contention.bpf.c */
 struct lock_contention_key {
-	u32 stack_id;
+	s32 stack_id;
 };
 
 struct lock_contention_data {
@@ -110,7 +110,7 @@ int lock_contention_stop(void)
 int lock_contention_read(struct lock_contention *con)
 {
 	int fd, stack;
-	u32 prev_key, key;
+	s32 prev_key, key;
 	struct lock_contention_data data;
 	struct lock_stat *st;
 	struct machine *machine = con->machine;
@@ -119,6 +119,8 @@ int lock_contention_read(struct lock_contention *con)
 	fd = bpf_map__fd(skel->maps.lock_stat);
 	stack = bpf_map__fd(skel->maps.stacks);
 
+	con->lost = skel->bss->lost;
+
 	prev_key = 0;
 	while (!bpf_map_get_next_key(fd, &prev_key, &key)) {
 		struct map *kmap;
diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index 67d46533e518..9e8b94eb6320 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -12,7 +12,7 @@
 #define MAX_ENTRIES  10240
 
 struct contention_key {
-	__u32 stack_id;
+	__s32 stack_id;
 };
 
 struct contention_data {
@@ -27,7 +27,7 @@ struct tstamp_data {
 	__u64 timestamp;
 	__u64 lock;
 	__u32 flags;
-	__u32 stack_id;
+	__s32 stack_id;
 };
 
 /* callstack storage  */
@@ -73,6 +73,9 @@ int enabled;
 int has_cpu;
 int has_task;
 
+/* error stat */
+unsigned long lost;
+
 static inline int can_record(void)
 {
 	if (has_cpu) {
@@ -116,6 +119,8 @@ int contention_begin(u64 *ctx)
 	pelem->flags = (__u32)ctx[1];
 	pelem->stack_id = bpf_get_stackid(ctx, &stacks, BPF_F_FAST_STACK_CMP);
 
+	if (pelem->stack_id < 0)
+		lost++;
 	return 0;
 }
 
diff --git a/tools/perf/util/lock-contention.h b/tools/perf/util/lock-contention.h
index b09fd6eb978a..d9fc5f076567 100644
--- a/tools/perf/util/lock-contention.h
+++ b/tools/perf/util/lock-contention.h
@@ -113,6 +113,7 @@ struct lock_contention {
 	struct machine *machine;
 	struct hlist_head *result;
 	unsigned long map_len;
+	unsigned long lost;
 };
 
 #ifdef HAVE_BPF_SKEL
-- 
2.37.1.455.g008518b4e5-goog