Re: [PATCH v2 2/3] perf: Reveal PMU type in fdinfo

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Nov 01, 2024 at 09:17:56PM +0000, Chun-Tse Shao wrote:
> It gives useful info on knowing which PMUs are reserved by this process.
> Also add extra attributes 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

Maybe 'perf_event_attr' would be appropriate as it's the name of the
struct.

> perf_event-attr.config: 0
> perf_event-attr.config1:        0
> perf_event-attr.config2:        0
> perf_event-attr.config3:        0

It's hard to pick which fields to show here but I'd say that those
config[123] are not used frequently at least for regular events.
Maybe just showing type and config is fine.

> 
> 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: 65536
> perf_event-attr.config1:        0
> perf_event-attr.config2:        0
> perf_event-attr.config3:        0
> ```
> 
> Signed-off-by: Chun-Tse Shao <ctshao@google.com>
> ---
>  kernel/events/core.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)

FYI usually the kernel changes are applied to a different tree than the
tools.

> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index cdd09769e6c56..c950b6fc92cda 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -55,6 +55,7 @@
>  #include <linux/pgtable.h>
>  #include <linux/buildid.h>
>  #include <linux/task_work.h>
> +#include <linux/seq_file.h>
> 
>  #include "internal.h"
> 
> @@ -6820,6 +6821,17 @@ 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:\t%llu\n", event->attr.config);

I'm not sure if all archs are happy with treating it as %llu.

Thanks,
Namhyung


> +	seq_printf(m, "perf_event-attr.config1:\t%llu\n", event->attr.config1);
> +	seq_printf(m, "perf_event-attr.config2:\t%llu\n", event->attr.config2);
> +	seq_printf(m, "perf_event-attr.config3:\t%llu\n", event->attr.config3);
> +}
> +
>  static const struct file_operations perf_fops = {
>  	.release		= perf_release,
>  	.read			= perf_read,
> @@ -6828,6 +6840,7 @@ static const struct file_operations perf_fops = {
>  	.compat_ioctl		= perf_compat_ioctl,
>  	.mmap			= perf_mmap,
>  	.fasync			= perf_fasync,
> +	.show_fdinfo		= perf_show_fdinfo,
>  };
> 
>  /*
> --
> 2.47.0.163.g1226f6d8fa-goog
>