[PATCH 2/2] tracing: add per-CPU memory usage statistics in tracefs

[Xiang Gao <gxxa03070307@gmail.com>]

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

Signed-off-by: Xiang Gao <gaoxiang17@xiaomi.com>
---
 Documentation/trace/ftrace.rst |  3 +++
 kernel/trace/trace.c           | 46 +++++++++++++++++++++++++++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index ff9d604dd1b8..694c9ed8f241 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -230,6 +230,9 @@ of ftrace. Here is a list of some of the key files:
 	    buffers: ...
 	    snapshot_buffers: ...
 
+	The same file is provided under trace_stats/per_cpu/cpuN/, reporting
+	only the buffers belonging to that CPU.
+
   buffer_subbuf_size_kb:
 
 	This sets or displays the sub buffer size. The ring buffer is broken up
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b343e03a6cf8..ea05077af4a0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5815,6 +5815,31 @@ static int trace_mem_show(struct seq_file *m, void *v)
 }
 DEFINE_SHOW_ATTRIBUTE(trace_mem);
 
+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.buffers,
+					  &stats.snapshot);
+
+	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, "buffers: %lu\n", stats.buffers >> 10);
+	seq_printf(m, "snapshot_buffers: %lu\n", stats.snapshot >> 10);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(trace_mem_per_cpu);
+
 #define LAST_BOOT_HEADER ((void *)1)
 
 static void *l_next(struct seq_file *m, void *v, loff_t *pos)
@@ -9236,7 +9261,9 @@ 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)
@@ -9244,6 +9271,23 @@ 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