linux-kernel - Re: [PATCH v5 07/17] perf ftrace: add option '--inherit' to trace children processes

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Date:   Fri, 17 Jul 2020 22:27:27 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Changbin Du <changbin.du@...il.com>, Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 07/17] perf ftrace: add option '--inherit' to trace
 children processes

On Mon, Jul 13, 2020 at 10:59:56AM +0900, Namhyung Kim wrote:
> On Sat, Jul 11, 2020 at 9:42 PM Changbin Du <changbin.du@...il.com> wrote:
> >
> > This adds an option '--inherit' to allow us trace children
> > processes spawned by our target.
> >
> > Signed-off-by: Changbin Du <changbin.du@...il.com>
> >
> > ---
> > v2: option name '--trace-children' -> '--inherit'.
> > ---
> >  tools/perf/Documentation/perf-ftrace.txt |  3 ++
> >  tools/perf/builtin-ftrace.c              | 38 ++++++++++++++++++++++++
> >  2 files changed, 41 insertions(+)
> >
> > diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> > index 98fe01d354d1..fd632bd9b2c1 100644
> > --- a/tools/perf/Documentation/perf-ftrace.txt
> > +++ b/tools/perf/Documentation/perf-ftrace.txt
> > @@ -61,6 +61,9 @@ OPTIONS
> >         Set the size of per-cpu tracing buffer, <size> is expected to
> >         be a number with appended unit character - B/K/M/G.
> >
> > +--inherit::
> > +       Trace children processes spawned by our target.
> > +
> >  -T::
> >  --trace-funcs=::
> >         Only trace functions given by the argument.  Multiple functions
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index 887e78b23a82..4efaa7b6a906 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -39,6 +39,7 @@ struct perf_ftrace {
> >         struct list_head        nograph_funcs;
> >         int                     graph_depth;
> >         unsigned long           percpu_buffer_size;
> > +       bool                    inherit;
> >  };
> >
> >  struct filter_entry {
> > @@ -177,9 +178,27 @@ static int write_tracing_file_int(const char *name, int value)
> >         return 0;
> >  }
> >
> > +static int write_tracing_option_file(const char *name, const char *val)
> > +{
> > +       char *file;
> > +       int ret;
> > +
> > +       if (asprintf(&file, "options/%s", name) < 0)
> > +               return -1;
> > +
> > +       ret = __write_tracing_file(file, val, false);
> > +       free(file);
> > +       return ret;
> > +}
> > +
> >  static int reset_tracing_cpu(void);
> >  static void reset_tracing_filters(void);
> >
> > +static void reset_tracing_options(struct perf_ftrace *ftrace __maybe_unused)
> > +{
> > +       write_tracing_option_file("function-fork", "0");
> > +}
> > +
> >  static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
> >  {
> >         if (write_tracing_file("tracing_on", "0") < 0)
> > @@ -198,6 +217,7 @@ static int reset_tracing_files(struct perf_ftrace *ftrace __maybe_unused)
> >                 return -1;
> >
> >         reset_tracing_filters();
> > +       reset_tracing_options(ftrace);
> >         return 0;
> >  }
> >
> > @@ -336,6 +356,17 @@ static int set_tracing_percpu_buffer_size(struct perf_ftrace *ftrace)
> >         return 0;
> >  }
> >
> > +static int set_tracing_trace_inherit(struct perf_ftrace *ftrace)
> > +{
> > +       if (!ftrace->inherit)
> > +               return 0;
> > +
> > +       if (write_tracing_option_file("function-fork", "1") < 0)
> > +               return -1;
> > +
> > +       return 0;
> > +}
> > +
> >  static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
> >  {
> >         char *trace_file;
> > @@ -405,6 +436,11 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
> >                 goto out_reset;
> >         }
> >
> > +       if (set_tracing_trace_inherit(ftrace) < 0) {
> > +               pr_err("failed to set tracing option function-fork\n");
> > +               goto out_reset;
> > +       }
> 
> Can we have set_tracing_options() here instead to make
> the __cmd_ftrace() shorter?  It'd set other options added later.
> It's also symmetric to reset_tracing_options().
>
I appended a patch to do this. Thanks for your suggestion.

> Thanks
> Namhyung
> 
> > +
> >         if (write_tracing_file("current_tracer", ftrace->tracer) < 0) {
> >                 pr_err("failed to set current_tracer to %s\n", ftrace->tracer);
> >                 goto out_reset;
> > @@ -599,6 +635,8 @@ int cmd_ftrace(int argc, const char **argv)
> >                     "Max depth for function graph tracer"),
> >         OPT_CALLBACK('m', "buffer-size", &ftrace.percpu_buffer_size, "size",
> >                      "size of per cpu buffer", parse_buffer_size),
> > +       OPT_BOOLEAN(0, "inherit", &ftrace.inherit,
> > +                   "trace children processes"),
> >         OPT_END()
> >         };
> >
> > --
> > 2.25.1
> >

-- 
Cheers,
Changbin Du