linux-kernel - Re: [PATCH] perf record: Disallow -c and -F option at the same time

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Date:   Tue, 4 May 2021 09:38:52 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Alexey Alexandrov <aalexand@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH] perf record: Disallow -c and -F option at the same time

Em Mon, May 03, 2021 at 02:32:32PM -0700, Namhyung Kim escreveu:
> Hi Arnaldo,
> 
> (Adjusting thetop-post)
> 
> On Sat, Apr 3, 2021 at 10:35 AM Alexey Alexandrov <aalexand@...gle.com> wrote:
> > On Sat, Apr 3, 2021, 10:13 Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> >>
> >> Em Fri, Apr 02, 2021 at 08:25:30PM -0700, Alexey Alexandrov escreveu:
> >> > A warning can be missed when the tool is run by some kind of automation.
> >> > Backward compatibility aside, I think conflicting flags should result in an
> >> > early exit to avoid later surprises.
> >>
> >> Sure, I agree with you in principle, but having erred out in the past,
> >> i.e. in making this be accepted, now making this out of the blue finally
> >> be considered what it always should have been considered, an error,
> >> feels like an error.
> >>
> >> I sent this message after merging the change, but before pushing it out
> >> publicly I felt some (more) discussion would be in order.
> >>
> >> Are you sure that potentially breaking existing scripts is ok in this
> >> case?
> >>
> >> Up to you, frankly.
> >
> > I personally think it's ok to break the existing conflicting usages of these flags because the owners of those invocations need to review and fix them to know what they are doing.
> >
> > At the same time, this can be a two-step movement: maybe first let's make it an error message that imperatively states the problem and makes it clear that the invocation needs to be fixed, then (after X months) make it an exiting error.
> 
> So what do you think?  I can make some changes if you want.
> But as it's rare and should be fixed anyway, I think we're good now.

Fair enough, I'm applying it as-is,

- Arnaldo
 
> Thanks,
> Namhyung
> 
> >
> >> > wrote:
> >> >
> >> > > Em Fri, Apr 02, 2021 at 06:40:20PM +0900, Namhyung Kim escreveu:
> >> > > > It's confusing which one is effective when the both options are given.
> >> > > > The current code happens to use -c in this case but users might not be
> >> > > > aware of it.  We can change it to complain about that instead of
> >> > > > relying on the implicit priority.
> >> > > >
> >> > > > Before:
> >> > > >   $ perf record -c 111111 -F 99 true
> >> > > >   [ perf record: Woken up 1 times to write data ]
> >> > > >   [ perf record: Captured and wrote 0.031 MB perf.data (8 samples) ]
> >> > > >
> >> > > >   $ perf evlist -F
> >> > > >   cycles: sample_period=111111
> >> > > >
> >> > > > After:
> >> > > >   $ perf record -c 111111 -F 99 true
> >> > > >   cannot set frequency and period at the same time
> >> > > >
> >> > > > So this change can break existing usages, but I think it's rare to
> >> > > > have both options and it'd be better changing them.
> >> > >
> >> > > Humm, perhaps we can just make that an warning stating that -c is used
> >> > > if both are specified?
> >> > >
> >> > > $ perf record -c 111111 -F 99 true
> >> > > Frequency and period can't be used the same time, -c 11111 will be used.
> >> > >
> >> > > - Arnaldo
> >> > >
> >> > > > Suggested-by: Alexey Alexandrov <aalexand@...gle.com>
> >> > > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> >> > > > ---
> >> > > >  tools/perf/util/record.c | 8 +++++++-
> >> > > >  1 file changed, 7 insertions(+), 1 deletion(-)
> >> > > >
> >> > > > diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
> >> > > > index f99852d54b14..43e5b563dee8 100644
> >> > > > --- a/tools/perf/util/record.c
> >> > > > +++ b/tools/perf/util/record.c
> >> > > > @@ -157,9 +157,15 @@ static int get_max_rate(unsigned int *rate)
> >> > > >  static int record_opts__config_freq(struct record_opts *opts)
> >> > > >  {
> >> > > >       bool user_freq = opts->user_freq != UINT_MAX;
> >> > > > +     bool user_interval = opts->user_interval != ULLONG_MAX;
> >> > > >       unsigned int max_rate;
> >> > > >
> >> > > > -     if (opts->user_interval != ULLONG_MAX)
> >> > > > +     if (user_interval && user_freq) {
> >> > > > +             pr_err("cannot set frequency and period at the same
> >> > > time\n");
> >> > > > +             return -1;
> >> > > > +     }
> >> > > > +
> >> > > > +     if (user_interval)
> >> > > >               opts->default_interval = opts->user_interval;
> >> > > >       if (user_freq)
> >> > > >               opts->freq = opts->user_freq;
> >> > > > --
> >> > > > 2.31.0.208.g409f899ff0-goog
> >> > > >
> >> > >
> >> > > --
> >> > >
> >> > > - Arnaldo
> >> > >
> >>
> >> --
> >>
> >> - Arnaldo

-- 

- Arnaldo