linux-kernel - Re: [PATCH] perf/ftrace: system_wide collection is not effective by default

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Date:   Thu, 27 Jan 2022 21:19:29 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Changbin Du <changbin.du@...il.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf/ftrace: system_wide collection is not effective by
 default

On Wed, Jan 26, 2022 at 03:47:48PM -0800, Namhyung Kim wrote:
> Hello,
> 
> On Wed, Jan 26, 2022 at 7:19 AM Changbin Du <changbin.du@...il.com> wrote:
> >
> > The ftrace.target.system_wide must be set before invoking
> > evlist__create_maps(), otherwise it has no effect.
> 
> Oh, right.  Thanks for pointing that out.
> 
> >
> > Fixes: 53be50282269 ("perf ftrace: Add 'latency' subcommand")
> > Signed-off-by: Changbin Du <changbin.du@...il.com>
> > ---
> >  tools/perf/builtin-ftrace.c | 45 ++++++++++++++++++++-----------------
> >  1 file changed, 24 insertions(+), 21 deletions(-)
> >
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index dec24dc0e767..26bff29ad277 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -1115,6 +1115,7 @@ enum perf_ftrace_subcommand {
> >  int cmd_ftrace(int argc, const char **argv)
> >  {
> >         int ret;
> > +       int (*cmd_func)(struct perf_ftrace *) = NULL;
> >         struct perf_ftrace ftrace = {
> >                 .tracer = DEFAULT_TRACER,
> >                 .target = { .uid = UINT_MAX, },
> > @@ -1221,6 +1222,28 @@ int cmd_ftrace(int argc, const char **argv)
> >                 goto out_delete_filters;
> >         }
> >
> > +       switch (subcmd) {
> > +       case PERF_FTRACE_TRACE:
> > +               if (!argc && target__none(&ftrace.target))
> > +                       ftrace.target.system_wide = true;
> 
> We can move only this part after parse_options().
>
I prefer that all parsing works get be done first. :)

> > +               cmd_func = __cmd_ftrace;
> > +               break;
> > +       case PERF_FTRACE_LATENCY:
> > +               if (list_empty(&ftrace.filters)) {
> > +                       pr_err("Should provide a function to measure\n");
> > +                       parse_options_usage(ftrace_usage, options, "T", 1);
> > +                       ret = -EINVAL;
> > +                       goto out_delete_evlist;
> 
> Otherwise, it should go to the out_delete_filters.
> 
yes, will fix it.

> > +               }
> > +               cmd_func = __cmd_latency;
> > +               break;
> > +       case PERF_FTRACE_NONE:
> > +       default:
> > +               pr_err("Invalid subcommand\n");
> > +               ret = -EINVAL;
> > +               goto out_delete_evlist;
> 
> Ditto.
> 
okay.

> Thanks,
> Namhyung
> 
> 
> > +       }
> > +
> >         ret = target__validate(&ftrace.target);
> >         if (ret) {
> >                 char errbuf[512];
> > @@ -1248,27 +1271,7 @@ int cmd_ftrace(int argc, const char **argv)
> >                         goto out_delete_evlist;
> >         }
> >
> > -       switch (subcmd) {
> > -       case PERF_FTRACE_TRACE:
> > -               if (!argc && target__none(&ftrace.target))
> > -                       ftrace.target.system_wide = true;
> > -               ret = __cmd_ftrace(&ftrace);
> > -               break;
> > -       case PERF_FTRACE_LATENCY:
> > -               if (list_empty(&ftrace.filters)) {
> > -                       pr_err("Should provide a function to measure\n");
> > -                       parse_options_usage(ftrace_usage, options, "T", 1);
> > -                       ret = -EINVAL;
> > -                       goto out_delete_evlist;
> > -               }
> > -               ret = __cmd_latency(&ftrace);
> > -               break;
> > -       case PERF_FTRACE_NONE:
> > -       default:
> > -               pr_err("Invalid subcommand\n");
> > -               ret = -EINVAL;
> > -               break;
> > -       }
> > +       ret = cmd_func(&ftrace);
> >
> >  out_delete_evlist:
> >         evlist__delete(ftrace.evlist);
> > --
> > 2.32.0
> >

-- 
Cheers,
Changbin Du