[PATCH 2/2] tracing: add per-CPU memory usage statistics in tracefs
From: Xiang Gao <hidden>
Date: 2026-09-05 11:27:58
Also in:
lkml
Subsystem:
documentation, function hooks (ftrace), the rest, tracing · Maintainers:
Jonathan Corbet, Steven Rostedt, Masami Hiramatsu, Linus Torvalds
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 <redacted> --- 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