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

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Date:   Wed, 05 Aug 2020 22:05:03 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Changbin Du <changbin.du@...il.com>
CC:     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 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

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