linux-kernel - Re: [PATCH 4/7] perf script: Add --inline option

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Message-ID: <20170524072142.cto7coohqwhake6t@gmail.com>
Date:   Wed, 24 May 2017 09:21:42 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Milian Wolff <milian.wolff@...b.com>,
        Yao Jin <yao.jin@...ux.intel.com>
Subject: Re: [PATCH 4/7] perf script: Add --inline option


* Namhyung Kim <namhyung@...nel.org> wrote:

> On Wed, May 24, 2017 at 08:38:11AM +0200, Ingo Molnar wrote:
> > 
> > * Namhyung Kim <namhyung@...nel.org> wrote:
> > 
> > > The --inline option is to show inlined functions in callchains.
> > > 
> > > For example,
> > > 
> > >   $ perf script
> > >   a.out  5644 11611.467597:     309961 cycles:u:
> > >                      790 main (/home/namhyung/tmp/perf/a.out)
> > >                    20511 __libc_start_main (/usr/lib/libc-2.25.so)
> > >                      8ba _start (/home/namhyung/tmp/perf/a.out)
> > >   ...
> > > 
> > >   $ perf script --inline
> > >   a.out  5644 11611.467597:     309961 cycles:u:
> > >                      790 main (/home/namhyung/tmp/perf/a.out)
> > >                          std::__detail::_Adaptor<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul>, double>::operator()
> > >                          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> >
> > >                          std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned long, 16807ul, 0ul, 2147483647ul> >
> > >                          main
> > >                    20511 __libc_start_main (/usr/lib/libc-2.25.so)
> > >                      8ba _start (/home/namhyung/tmp/perf/a.out)
> > >   ...
> > 
> > Shouldn't this be the default behavior, to make call chains more readable?
> 
> AFAIK perf report didn't make it default due to a performance impact,
> but I didn't know how much it is.  Especially if perf was not built
> with libbfd it'll run external addr2line to get inlined functions for
> each callchain entry..

So then at least let's make it the default when all libraries are present. Not 
enabling something when the build is not 'complete' is fair game - distros will 
typically have all the libraries available.

We need to remember that roughly 99% of all our users will use as few perf command 
line options as they can get away with - myself included. Adding a non-debugging 
feature as a non-default command line option is really as if we didn't do 
anything: very few if any people will use it, and it might bitrot in the future 
without people noticing.

So we need apply some thought into making it available to two orders of magnitude 
more people! If someone types 'perf report' we should give the best selection of 
all the features we have available.

Thanks,

	Ingo