linux-kernel - Re: [PATCH v7 01/18] perf ftrace: select function/function

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Message-ID: <20200808022203.yqadm2verquocjrg@mail.google.com>
Date:   Sat, 8 Aug 2020 10:22:03 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Changbin Du <changbin.du@...il.com>, Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 01/18] perf ftrace: select function/function_graph
 tracer automatically

On Wed, Aug 05, 2020 at 10:05:03PM -0300, Arnaldo Carvalho de Melo wrote:
> 
> 
> On August 5, 2020 9:14:48 PM GMT-03:00, Changbin Du <changbin.du@...il.com> wrote:
> >On Tue, Aug 04, 2020 at 09:51:15AM -0300, Arnaldo Carvalho de Melo
> >wrote:
> >> Em Sat, Jul 18, 2020 at 02:48:09PM +0800, Changbin Du escreveu:
> >> > The '-g/-G' options have already implied function_graph tracer
> >should be
> >> > used instead of function tracer. So the extra option '--tracer' can
> >be
> >> > killed.
> >> > 
> >> > This patch changes the behavior as below:
> >> >   - By default, function tracer is used.
> >> >   - If '-g' or '-G' option is on, then function_graph tracer is
> >used.
> >> >   - The perf configuration item 'ftrace.tracer' is marked as
> >deprecated.
> >> >   - The option '--tracer' is marked as deprecated.
> >> 
> >> You should try to be more granular, for instance, I think the
> >decision
> >> to change the default is questionable, but could be acceptable.
> >> 
> >> But why deprecate the perf configuration for the default tracer?
> >> 
> >> Say people who already use 'perf ftrace ls' go and use with this
> >patch
> >> and see that it changed the default from the function_graph tracer to
> >> the function tracer and disagree with you, they want the default to
> >be
> >> the function graph tracer, know that there is (or there was) a
> >> ftrace.tracer in ~/.prefconfig, and then try that, only to find out
> >that
> >> it is not possible, frustrating :-\
> >> 
> >> So can we please remove this deprecation of ftrace.tracer so that
> >people
> >> used to how it was can get that behaviour back?
> >> 
> >Agreed. If no -F or -G is given, we can use the ftrace.tracer as
> >default tracer.
> >Let me update it. Thanks.
> 
> Thanks, I'm general try to be as granular as possible, doing one thing per patch, this way the reviewer can do some preliminary cherry picking and we also improve git bisectability.
>
Arnaldo, I changed the policy as below:
      - Preserve the default tracerr which is function_graph.
      - If '-g' or '-G' option is on, then function_graph tracer is used.
      - If '-T' or '-N' option is on, then function tracer is used.
      - The option '--tracer' or configuration ftrace.tracer only takes
	effect if neither -g/-G nor -T/-N is specified.
      - The function_graph has priority over function tracer if both -G/-g
	and -T/-N are given.

Please check updatae in v8. Thanks.
> - Arnaldo
> 
> -- 
> Sent from my Android device with K-9 Mail. Please excuse my brevity.

-- 
Cheers,
Changbin Du