linux-kernel - [PATCH v5 1/2] perf: Reveal PMU type in fdinfo

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Message-ID: <20251121230951.3240124-1-ctshao@google.com>
Date: Fri, 21 Nov 2025 15:09:11 -0800
From: Chun-Tse Shao <ctshao@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Chun-Tse Shao <ctshao@...gle.com>, Ian Rogers <irogers@...gle.com>, peterz@...radead.org, 
	mingo@...hat.com, acme@...nel.org, namhyung@...nel.org, mark.rutland@....com, 
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org, adrian.hunter@...el.com, 
	thomas.falcon@...el.com, kan.liang@...ux.intel.com, howardchu95@...il.com, 
	linux-perf-users@...r.kernel.org
Subject: [PATCH v5 1/2] perf: Reveal PMU type in fdinfo

It gives useful info on knowing which PMUs are reserved by this process.
Also add config which would be useful.
Testing cycles:

  $ ./perf stat -e cycles &
  $ cat /proc/`pidof perf`/fdinfo/3
  pos:    0
  flags:  02000002
  mnt_id: 16
  ino:    3081
  perf_event_attr.type:   0
  perf_event_attr.config: 0x0
  perf_event_attr.config1:        0x0
  perf_event_attr.config2:        0x0
  perf_event_attr.config3:        0x0

Testing L1-dcache-load-misses:

  $ ./perf stat -e L1-dcache-load-misses &
  $ cat /proc/`pidof perf`/fdinfo/3
  pos:    0
  flags:  02000002
  mnt_id: 16
  ino:    1072
  perf_event_attr.type:   3
  perf_event_attr.config: 0x10000
  perf_event_attr.config1:        0x0
  perf_event_attr.config2:        0x0
  perf_event_attr.config3:        0x0

Reviewed-by: Ian Rogers <irogers@...gle.com>
Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
---
v5:
  Added config1, config2 and config3 and print output in hex.

v4:
  lore.kernel.org/20250603181634.1362626-1-ctshao@...gle.com/
  Removed the first patch in v3 since it is merged.
  Retested to make sure the patch still work.

v3: lore.kernel.org/20241106003007.2112584-3-ctshao@...gle.com/

 kernel/events/core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7541f6f85fcb..17a71fe1d538 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -56,6 +56,7 @@
 #include <linux/buildid.h>
 #include <linux/task_work.h>
 #include <linux/percpu-rwsem.h>
+#include <linux/seq_file.h>

 #include "internal.h"

@@ -7212,6 +7213,20 @@ static int perf_fasync(int fd, struct file *filp, int on)
 	return 0;
 }

+static void perf_show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct perf_event *event = f->private_data;
+
+	seq_printf(m, "perf_event_attr.type:\t%u\n", event->orig_type);
+	seq_printf(m, "perf_event_attr.config:\t0x%llx\n", (unsigned long long)event->attr.config);
+	seq_printf(m, "perf_event_attr.config1:\t0x%llx\n",
+		   (unsigned long long)event->attr.config1);
+	seq_printf(m, "perf_event_attr.config2:\t0x%llx\n",
+		   (unsigned long long)event->attr.config2);
+	seq_printf(m, "perf_event_attr.config3:\t0x%llx\n",
+		   (unsigned long long)event->attr.config3);
+}
+
 static const struct file_operations perf_fops = {
 	.release		= perf_release,
 	.read			= perf_read,
@@ -7220,6 +7235,7 @@ static const struct file_operations perf_fops = {
 	.compat_ioctl		= perf_compat_ioctl,
 	.mmap			= perf_mmap,
 	.fasync			= perf_fasync,
+	.show_fdinfo		= perf_show_fdinfo,
 };

 /*
--
2.52.0.rc2.455.g230fcf2819-goog