linux-kernel - Re: [PATCH v4 1/2] perf: Reveal PMU type in fdinfo

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Message-ID: <CAP-5=fX0-W5BKha32qZu5zhJN=7Jvocz+ZwxLzXxYw_g2Zsz4Q@mail.gmail.com>
Date: Wed, 12 Nov 2025 08:59:51 -0800
From: Ian Rogers <irogers@...gle.com>
To: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
Cc: Chun-Tse Shao <ctshao@...gle.com>, linux-kernel@...r.kernel.org, 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, 
	kan.liang@...ux.intel.com, james.clark@...aro.org, howardchu95@...il.com, 
	weilin.wang@...el.com, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v4 1/2] perf: Reveal PMU type in fdinfo

On Mon, Sep 29, 2025 at 8:12 PM Mi, Dapeng <dapeng1.mi@...ux.intel.com> wrote:
>
>
> On 6/4/2025 2:15 AM, Chun-Tse Shao wrote:
> > 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: 0
> >
> > 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
> >
> > Reviewed-by: Ian Rogers <irogers@...gle.com>
> > Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
> > ---
> > v4:
> >   Removed the first patch in v3 since it is merged.
> >   Retested to make sure the patch still work.
> >
> > v3: lore.kernel.org/20241106003007.2112584-2-ctshao@...gle.com
> >
> >  kernel/events/core.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 95e703891b24..bad563692d63 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"
> >
> > @@ -7077,6 +7078,14 @@ 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", (unsigned long long)event->attr.config);
>
> Could we print the config field with hexadecimal format? It makes the event
> is more easily recognized. Thanks.

I think this is a reasonable suggestion. I think it would also be
useful to dump the config1, config2 and config3 values. I also think
the state of the event would be useful for debugging.

Thanks,
Ian

> > +}
> > +
> >  static const struct file_operations perf_fops = {
> >       .release                = perf_release,
> >       .read                   = perf_read,
> > @@ -7085,6 +7094,7 @@ static const struct file_operations perf_fops = {
> >       .compat_ioctl           = perf_compat_ioctl,
> >       .mmap                   = perf_mmap,
> >       .fasync                 = perf_fasync,
> > +     .show_fdinfo            = perf_show_fdinfo,
> >  };
> >
> >  /*
> > --
> > 2.49.0.1204.g71687c7c1d-goog
> >
> >