[PATCH 09/21] perf: Export running sample length values through debugfs

Jiri Olsa
2018-01-24T11:55:35Z

Exporting running_sample_length value through the debugfs,
via per cpu files:
/sys/kernel/debug/irq/cpuX/sample_length

and reset file to zero it:
/sys/kernel/debug/irq/reset

to allow some basic meassurements of the NMI time length.

Link: http://lkml.kernel.org/n/tip-uodlhfk3zc55fyajtlczr5wd@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
kernel/events/core.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 67 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4676fbf681c7..582913b7aba9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -51,6 +51,7 @@
#include <linux/proc_ns.h>
#include <linux/mount.h>
#include <linux/task_work.h>
+#include <linux/debugfs.h>

#include "internal.h"

@@ -554,6 +555,72 @@ void perf_sample_event_took(u64 sample_len_ns)
}
}

+static int get_sample_length(void *data, u64 *val)
+{
+ unsigned long cpu = (unsigned long) data;
+
+ *val = per_cpu(running_sample_length, cpu);
+ return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(sample_length_fops, get_sample_length, NULL, "%llu\n");
+
+
+static int reset_sample_length(void *data, u64 val)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ per_cpu(running_sample_length, cpu) = val;
+ }
+
+ return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(reset_fops, NULL, reset_sample_length, "%llu\n");
+
+static __init int init_perf_debugfs(void)
+{
+ struct dentry *root, *irq, *icpu, *file;
+ int cpu, ret = 0;
+
+ root = debugfs_create_dir("perf", NULL);
+ if (!root)
+ return -1;
+
+ irq = debugfs_create_dir("irq", root);
+ if (!irq)
+ return -1;
+
+ for_each_possible_cpu(cpu) {
+ char buf[50];
+
+ snprintf(buf, sizeof(buf), "cpu%d", cpu);
+
+ icpu = debugfs_create_dir(buf, irq);
+ if (!icpu)
+ return -1;
+
+ file = debugfs_create_file("sample_length", 0444, icpu,
+ (void *)(unsigned long) cpu,
+ &sample_length_fops);
+ if (!file) {
+ ret = -1;
+ break;
+ }
+ }
+
+ if (!ret) {
+ file = debugfs_create_file("reset", S_IWUSR, irq, NULL, &reset_fops);
+ if (!file)
+ ret = -1;
+ }
+
+ return ret;
+}
+
+late_initcall(init_perf_debugfs);
+
static atomic64_t perf_event_id;

static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx,
--
2.13.6