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

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Message-ID: <CAJpZYjVrTsuSwT-31hBYihzmK94j6BWGD4XxudTXMB0W+Hcb+g@mail.gmail.com>
Date: Tue, 5 Nov 2024 16:32:22 -0800
From: Chun-Tse Shao <ctshao@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Liang Kan <kan.liang@...ux.intel.com>, Ze Gao <zegao2021@...il.com>, 
	Weilin Wang <weilin.wang@...el.com>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 2/3] perf: Reveal PMU type in fdinfo

Thanks for your review, Namhyung! Here is the link to patch v3:
https://lore.kernel.org/all/20241106003007.2112584-2-ctshao@google.com/

On Mon, Nov 4, 2024 at 4:12 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> 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.
>

Agree.

> > 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.
>

Agree, it should be fine to add more if needed.

> >
> > 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@...gle.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.
>

Thanks for the heads up!

> >
> > 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.
>

I think with type casting to `unsigned long long`, it will make it
print in `%llu` for all archs.


> 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
> >