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

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Date:   Wed, 24 May 2017 09:53:49 +0200
From:   Milian Wolff <milian.wolff@...b.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Yao Jin <yao.jin@...ux.intel.com>
Subject: Re: [PATCH 4/7] perf script: Add --inline option

On Wednesday, May 24, 2017 9:21:42 AM CEST Ingo Molnar wrote:
> * 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_congruent
> > > >                          ial_engine<unsigned long, 16807ul, 0ul,
> > > >                          2147483647ul>, double>::operator()
> > > >                          std::uniform_real_distribution<double>::oper
> > > >                          ator()<std::linear_congruential_engine<unsign
> > > >                          ed long, 16807ul, 0ul, 2147483647ul> >
> > > >                          std::uniform_real_distribution<double>::oper
> > > >                          ator()<std::linear_congruential_engine<unsign
> > > >                          ed 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.

Just a suggestion: My larger patch set that is in review now adds some caching 
features which already speeds up the whole process considerably. As such, my 
suggestion is to wait for this patch set to be integrated. Then we could 
enable --inline unconditionally, or at least only when libbfd is available.

Cheers

-- 
Milian Wolff | milian.wolff@...b.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts
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