linux-kernel - [PATCH 4/4] locking/lockdep: Report more stack trace statistics

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Message-Id: <20190722182443.216015-5-bvanassche@acm.org>
Date:   Mon, 22 Jul 2019 11:24:43 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Bart Van Assche <bvanassche@....org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 4/4] locking/lockdep: Report more stack trace statistics

Report the number of stack traces and the number of stack trace hash
chains. These two numbers are useful because these allow to estimate
the number of stack trace hash collisions.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will.deacon@....com>
Cc: Waiman Long <longman@...hat.com>
Signed-off-by: Bart Van Assche <bvanassche@....org>
---
 kernel/locking/lockdep.c           | 29 +++++++++++++++++++++++++++++
 kernel/locking/lockdep_internals.h |  4 ++++
 kernel/locking/lockdep_proc.c      |  6 ++++++
 3 files changed, 39 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 19eace34b5fa..320346b3bdbb 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -516,6 +516,35 @@ static struct lock_trace *save_trace(void)
 
 	return trace;
 }
+
+/* Return the number of stack traces in the stack_trace[] array. */
+u64 lockdep_stack_trace_count(void)
+{
+	struct lock_trace *trace;
+	u64 c = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++) {
+		hlist_for_each_entry(trace, &stack_trace_hash[i], hash_entry) {
+			c++;
+		}
+	}
+
+	return c;
+}
+
+/* Return the number of stack hash chains that have at least one stack trace. */
+u64 lockdep_stack_hash_count(void)
+{
+	u64 c = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++)
+		if (!hlist_empty(&stack_trace_hash[i]))
+			c++;
+
+	return c;
+}
 #endif
 
 unsigned int nr_hardirq_chains;
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 93a008bf77db..18d85aebbb57 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -140,6 +140,10 @@ extern unsigned int max_bfs_queue_depth;
 #ifdef CONFIG_PROVE_LOCKING
 extern unsigned long lockdep_count_forward_deps(struct lock_class *);
 extern unsigned long lockdep_count_backward_deps(struct lock_class *);
+#ifdef CONFIG_TRACE_IRQFLAGS
+u64 lockdep_stack_trace_count(void);
+u64 lockdep_stack_hash_count(void);
+#endif
 #else
 static inline unsigned long
 lockdep_count_forward_deps(struct lock_class *class)
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 1ba5780182e7..64b5b47ab117 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -284,6 +284,12 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
 			nr_process_chains);
 	seq_printf(m, " stack-trace entries:           %11lu [max: %lu]\n",
 			nr_stack_trace_entries, MAX_STACK_TRACE_ENTRIES);
+#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
+	seq_printf(m, " number of stack traces:        %llu\n",
+		   lockdep_stack_trace_count());
+	seq_printf(m, " number of stack hash chains:   %llu\n",
+		   lockdep_stack_hash_count());
+#endif
 	seq_printf(m, " combined max dependencies:     %11u\n",
 			(nr_hardirq_chains + 1) *
 			(nr_softirq_chains + 1) *
-- 
2.22.0.657.g960e92d24f-goog