[PATCH v5 3/4] tracing: add per-CPU buffer memory usage statistics

[Xiang Gao]

Provide a per-CPU view of the tracing ring-buffer memory usage under
trace_stats/per_cpu/cpuN/memory_usage_kb, using the same categorized
format as the aggregate file. Each file reports only the buffers
belonging to that CPU.

Signed-off-by: Xiang Gao <gaoxiang17@xxxxxxxxxx>
---
 kernel/trace/trace.c | 75 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 74 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6036e368fe10..e7e23ff38105 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5898,6 +5898,60 @@ static const struct file_operations trace_mem_fops = {
 	.release	= single_release,
 };
 
+static struct trace_mem_stats trace_buffers_memory_cpu(int cpu)
+{
+	struct trace_mem_stats stats = {};
+	struct trace_array *tr;
+
+	guard(mutex)(&trace_types_lock);
+
+	list_for_each_entry(tr, &ftrace_trace_arrays, list)
+		trace_array_buffer_memory(tr, cpu, &stats);
+
+	/* Account for the bootstrapping temp_buffer as well. */
+	if (temp_buffer)
+		stats.global += ring_buffer_memory_size(temp_buffer, cpu);
+
+	stats.total_system = stats.global + stats.instances +
+			     stats.snapshots + stats.remotes;
+	stats.total_carveout = stats.persistents;
+
+	return stats;
+}
+
+static int trace_mem_per_cpu_show(struct seq_file *m, void *v)
+{
+	struct trace_mem_stats stats = trace_buffers_memory_cpu((long)m->private);
+
+	seq_printf(m, "global: %lu\n", stats.global >> 10);
+	seq_printf(m, "instances: %lu\n", stats.instances >> 10);
+	seq_printf(m, "snapshots: %lu\n", stats.snapshots >> 10);
+	seq_printf(m, "persistents: %lu\n", stats.persistents >> 10);
+	seq_printf(m, "remotes: %lu\n", stats.remotes >> 10);
+	seq_printf(m, "total_system: %lu\n", stats.total_system >> 10);
+	seq_printf(m, "total_carveout: %lu\n", stats.total_carveout >> 10);
+
+	return 0;
+}
+
+static int trace_mem_per_cpu_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	ret = tracing_check_open_get_tr(NULL);
+	if (ret)
+		return ret;
+
+	return single_open(file, trace_mem_per_cpu_show, inode->i_private);
+}
+
+static const struct file_operations trace_mem_per_cpu_fops = {
+	.open		= trace_mem_per_cpu_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 #define LAST_BOOT_HEADER ((void *)1)
 
 static void *l_next(struct seq_file *m, void *v, loff_t *pos)
@@ -9416,7 +9470,9 @@ static struct notifier_block trace_module_nb = {
 
 static __init void init_trace_stats_tracefs(void)
 {
-	struct dentry *stats_dir;
+	struct dentry *stats_dir, *per_cpu_dir, *cpu_dir;
+	char cpu_dir_name[30];
+	int cpu;
 
 	stats_dir = tracefs_create_dir("trace_stats", NULL);
 	if (!stats_dir)
@@ -9424,6 +9480,23 @@ static __init void init_trace_stats_tracefs(void)
 
 	trace_create_file("memory_usage_kb", TRACE_MODE_READ, stats_dir,
 			  NULL, &trace_mem_fops);
+
+	per_cpu_dir = tracefs_create_dir("per_cpu", stats_dir);
+	if (!per_cpu_dir)
+		return;
+
+	for_each_tracing_cpu(cpu) {
+		snprintf(cpu_dir_name, 30, "cpu%d", cpu);
+		cpu_dir = tracefs_create_dir(cpu_dir_name, per_cpu_dir);
+		if (!cpu_dir) {
+			pr_warn("Could not create tracefs '%s' entry\n",
+				cpu_dir_name);
+			continue;
+		}
+
+		trace_create_file("memory_usage_kb", TRACE_MODE_READ, cpu_dir,
+				  (void *)(long)cpu, &trace_mem_per_cpu_fops);
+	}
 }
 
 static __init void tracer_init_tracefs_work_func(struct work_struct *work)
-- 
2.34.1